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 $208.87   11.146%   $232.1507   $232.15   $232.15   $232.20  
  Purchase #2 $203.65   9.838%   $223.6851   $223.69   $223.70   $223.70  
  Purchase #3 $169.85   4.725%   $177.8754   $177.88   $177.90   $177.90  
  Purchase #4 $24.58   4.752%   $25.748   $25.75   $25.75   $25.70  
  Purchase #5 $56.88   6.253%   $60.4367   $60.44   $60.45   $60.40  
  Purchase #6 $54.67   12.580%   $61.5475   $61.55   $61.55   $61.50  
  Purchase #7 $157.25   8.642%   $170.8395   $170.84   $170.85   $170.80  
  7 purchase totals = $875.75       $952.2829   $952.30   $952.35   $952.20