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 $95.33   9.253%   $104.1509   $104.15   $104.15   $104.20  
  Purchase #2 $123.74   5.344%   $130.3527   $130.35   $130.35   $130.40  
  Purchase #3 $158.40   7.859%   $170.8487   $170.85   $170.85   $170.80  
  Purchase #4 $236.52   12.135%   $265.2217   $265.22   $265.20   $265.20  
  Purchase #5 $81.63   12.281%   $91.655   $91.66   $91.65   $91.70  
  Purchase #6 $155.87   8.641%   $169.3387   $169.34   $169.35   $169.30  
  Purchase #7 $30.70   3.695%   $31.8344   $31.83   $31.85   $31.80  
  7 purchase totals = $882.19       $963.4021   $963.40   $963.40   $963.40