Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $191.85   13.746%   $218.2217   $218.22   $218.20   $218.20  
  Purchase #2 $125.96   3.389%   $130.2288   $130.23   $130.25   $130.20  
  Purchase #3 $115.27   9.739%   $126.4961   $126.50   $126.50   $126.50  
  Purchase #4 $203.26   9.659%   $222.8929   $222.89   $222.90   $222.90  
  Purchase #5 $167.78   12.557%   $188.8481   $188.85   $188.85   $188.80  
  Purchase #6 $237.92   12.360%   $267.3269   $267.33   $267.35   $267.30  
  Purchase #7 $184.85   10.107%   $203.5328   $203.53   $203.55   $203.50  
  7 purchase totals = $1,226.89       $1,357.5473   $1,357.55   $1,357.60   $1,357.40