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 $233.75   12.495%   $262.9571   $262.96   $262.95   $263.00  
  Purchase #2 $69.80   8.422%   $75.6786   $75.68   $75.70   $75.70  
  Purchase #3 $134.54   7.686%   $144.8807   $144.88   $144.90   $144.90  
  Purchase #4 $137.79   10.473%   $152.2207   $152.22   $152.20   $152.20  
  Purchase #5 $37.49   10.350%   $41.3702   $41.37   $41.35   $41.40  
  Purchase #6 $100.98   4.733%   $105.7594   $105.76   $105.75   $105.80  
  Purchase #7 $65.76   12.809%   $74.1832   $74.18   $74.20   $74.20  
  7 purchase totals = $780.11       $857.0499   $857.05   $857.05   $857.20