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 $193.31   4.235%   $201.4967   $201.50   $201.50   $201.50  
  Purchase #2 $211.74   11.534%   $236.1621   $236.16   $236.15   $236.20  
  Purchase #3 $119.43   8.744%   $129.873   $129.87   $129.85   $129.90  
  Purchase #4 $94.40   13.438%   $107.0855   $107.09   $107.10   $107.10  
  Purchase #5 $188.98   11.352%   $210.433   $210.43   $210.45   $210.40  
  Purchase #6 $222.49   3.304%   $229.8411   $229.84   $229.85   $229.80  
  Purchase #7 $126.56   13.829%   $144.062   $144.06   $144.05   $144.10  
  7 purchase totals = $1,156.91       $1,258.9534   $1,258.95   $1,258.95   $1,259.00