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 $136.93   11.510%   $152.6906   $152.69   $152.70   $152.70  
  Purchase #2 $73.88   4.138%   $76.9372   $76.94   $76.95   $76.90  
  Purchase #3 $191.48   10.414%   $211.4207   $211.42   $211.40   $211.40  
  Purchase #4 $88.97   3.433%   $92.0243   $92.02   $92.00   $92.00  
  Purchase #5 $11.95   6.552%   $12.733   $12.73   $12.75   $12.70  
  Purchase #6 $248.49   4.727%   $260.2361   $260.24   $260.25   $260.20  
  Purchase #7 $115.47   3.826%   $119.8879   $119.89   $119.90   $119.90  
  7 purchase totals = $867.17       $925.9298   $925.93   $925.95   $925.80