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 $23.93   7.661%   $25.7633   $25.76   $25.75   $25.80  
  Purchase #2 $155.60   3.165%   $160.5247   $160.52   $160.50   $160.50  
  Purchase #3 $30.29   8.538%   $32.8762   $32.88   $32.90   $32.90  
  Purchase #4 $76.29   5.531%   $80.5096   $80.51   $80.50   $80.50  
  Purchase #5 $125.40   13.136%   $141.8725   $141.87   $141.85   $141.90  
  Purchase #6 $85.29   7.103%   $91.3481   $91.35   $91.35   $91.30  
  Purchase #7 $182.34   8.318%   $197.507   $197.51   $197.50   $197.50  
  7 purchase totals = $679.14       $730.4014   $730.40   $730.35   $730.40