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 $60.39   4.200%   $62.9264   $62.93   $62.95   $62.90  
  Purchase #2 $182.65   7.224%   $195.8446   $195.84   $195.85   $195.80  
  Purchase #3 $176.31   11.821%   $197.1516   $197.15   $197.15   $197.20  
  Purchase #4 $238.63   10.327%   $263.2733   $263.27   $263.25   $263.30  
  Purchase #5 $133.38   9.701%   $146.3192   $146.32   $146.30   $146.30  
  Purchase #6 $143.84   11.564%   $160.4737   $160.47   $160.45   $160.50  
  Purchase #7 $66.51   11.709%   $74.2977   $74.30   $74.30   $74.30  
  7 purchase totals = $1,001.71       $1,100.2865   $1,100.28   $1,100.25   $1,100.30