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 $201.63   11.174%   $224.1601   $224.16   $224.15   $224.20  
  Purchase #2 $144.73   9.654%   $158.7022   $158.70   $158.70   $158.70  
  Purchase #3 $211.51   5.408%   $222.9485   $222.95   $222.95   $222.90  
  Purchase #4 $102.56   13.836%   $116.7502   $116.75   $116.75   $116.80  
  Purchase #5 $104.80   3.463%   $108.4292   $108.43   $108.45   $108.40  
  Purchase #6 $42.71   13.386%   $48.4272   $48.43   $48.45   $48.40  
  Purchase #7 $16.98   9.207%   $18.5433   $18.54   $18.55   $18.50  
  7 purchase totals = $824.92       $897.9607   $897.96   $898.00   $897.90