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 $96.98   10.561%   $107.2221   $107.22   $107.20   $107.20  
  Purchase #2 $92.95   6.807%   $99.2771   $99.28   $99.30   $99.30  
  Purchase #3 $62.44   9.150%   $68.1533   $68.15   $68.15   $68.20  
  Purchase #4 $83.61   11.580%   $93.292   $93.29   $93.30   $93.30  
  Purchase #5 $48.84   5.557%   $51.554   $51.55   $51.55   $51.60  
  Purchase #6 $20.44   13.490%   $23.1974   $23.20   $23.20   $23.20  
  Purchase #7 $154.38   3.802%   $160.2495   $160.25   $160.25   $160.20  
  7 purchase totals = $559.64       $602.9454   $602.94   $602.95   $603.00