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 $234.68   13.279%   $265.8432   $265.84   $265.85   $265.80  
  Purchase #2 $119.63   3.398%   $123.695   $123.70   $123.70   $123.70  
  Purchase #3 $249.72   11.457%   $278.3304   $278.33   $278.35   $278.30  
  Purchase #4 $184.43   5.623%   $194.8005   $194.80   $194.80   $194.80  
  Purchase #5 $118.73   6.460%   $126.4   $126.40   $126.40   $126.40  
  Purchase #6 $195.34   4.223%   $203.5892   $203.59   $203.60   $203.60  
  Purchase #7 $30.25   10.254%   $33.3518   $33.35   $33.35   $33.40  
  7 purchase totals = $1,132.78       $1,226.0101   $1,226.01   $1,226.05   $1,226.00