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 $55.84   11.266%   $62.1309   $62.13   $62.15   $62.10  
  Purchase #2 $194.39   12.472%   $218.6343   $218.63   $218.65   $218.60  
  Purchase #3 $67.97   8.231%   $73.5646   $73.56   $73.55   $73.60  
  Purchase #4 $222.51   4.568%   $232.6743   $232.67   $232.65   $232.70  
  Purchase #5 $94.38   9.647%   $103.4848   $103.48   $103.50   $103.50  
  Purchase #6 $162.96   10.254%   $179.6699   $179.67   $179.65   $179.70  
  Purchase #7 $87.68   7.534%   $94.2858   $94.29   $94.30   $94.30  
  7 purchase totals = $885.73       $964.4446   $964.43   $964.45   $964.50