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 $244.39   9.227%   $266.9399   $266.94   $266.95   $266.90  
  Purchase #2 $29.46   13.252%   $33.364   $33.36   $33.35   $33.40  
  Purchase #3 $87.89   10.117%   $96.7818   $96.78   $96.80   $96.80  
  Purchase #4 $131.89   4.874%   $138.3183   $138.32   $138.30   $138.30  
  Purchase #5 $119.28   3.117%   $122.998   $123.00   $123.00   $123.00  
  Purchase #6 $234.53   4.228%   $244.4459   $244.45   $244.45   $244.40  
  Purchase #7 $21.56   3.252%   $22.2611   $22.26   $22.25   $22.30  
  7 purchase totals = $869.00       $925.1090   $925.11   $925.10   $925.10