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 $55.89   5.427%   $58.9232   $58.92   $58.90   $58.90  
  Purchase #2 $170.71   7.751%   $183.9417   $183.94   $183.95   $183.90  
  Purchase #3 $130.39   12.715%   $146.9691   $146.97   $146.95   $147.00  
  Purchase #4 $228.55   3.708%   $237.0246   $237.02   $237.00   $237.00  
  Purchase #5 $19.56   6.103%   $20.7537   $20.75   $20.75   $20.80  
  Purchase #6 $201.51   11.205%   $224.0892   $224.09   $224.10   $224.10  
  Purchase #7 $76.94   9.432%   $84.197   $84.20   $84.20   $84.20  
  7 purchase totals = $883.55       $955.8985   $955.89   $955.85   $955.90