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 $54.29   10.873%   $60.193   $60.19   $60.20   $60.20  
  Purchase #2 $125.46   9.115%   $136.8957   $136.90   $136.90   $136.90  
  Purchase #3 $59.33   8.265%   $64.2336   $64.23   $64.25   $64.20  
  Purchase #4 $239.67   9.473%   $262.3739   $262.37   $262.35   $262.40  
  Purchase #5 $235.50   7.531%   $253.2355   $253.24   $253.25   $253.20  
  Purchase #6 $39.94   6.431%   $42.5085   $42.51   $42.50   $42.50  
  Purchase #7 $54.94   5.456%   $57.9375   $57.94   $57.95   $57.90  
  7 purchase totals = $809.13       $877.3777   $877.38   $877.40   $877.30