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 $43.89   9.419%   $48.024   $48.02   $48.00   $48.00  
  Purchase #2 $144.35   4.300%   $150.5571   $150.56   $150.55   $150.60  
  Purchase #3 $127.63   12.441%   $143.5084   $143.51   $143.50   $143.50  
  Purchase #4 $179.51   8.232%   $194.2873   $194.29   $194.30   $194.30  
  Purchase #5 $168.78   11.569%   $188.3062   $188.31   $188.30   $188.30  
  Purchase #6 $56.68   5.833%   $59.9861   $59.99   $60.00   $60.00  
  Purchase #7 $227.28   10.763%   $251.7421   $251.74   $251.75   $251.70  
  7 purchase totals = $948.12       $1,036.4112   $1,036.42   $1,036.40   $1,036.40