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 $232.33   11.321%   $258.6321   $258.63   $258.65   $258.60  
  Purchase #2 $247.56   4.187%   $257.9253   $257.93   $257.95   $257.90  
  Purchase #3 $227.39   8.198%   $246.0314   $246.03   $246.05   $246.00  
  Purchase #4 $99.35   7.836%   $107.1351   $107.14   $107.15   $107.10  
  Purchase #5 $25.30   4.741%   $26.4995   $26.50   $26.50   $26.50  
  Purchase #6 $96.46   8.131%   $104.3032   $104.30   $104.30   $104.30  
  Purchase #7 $229.61   8.793%   $249.7996   $249.80   $249.80   $249.80  
  7 purchase totals = $1,158.00       $1,250.3262   $1,250.33   $1,250.40   $1,250.20