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 $233.59   12.265%   $262.2398   $262.24   $262.25   $262.20  
  Purchase #2 $57.25   9.827%   $62.876   $62.88   $62.90   $62.90  
  Purchase #3 $70.42   7.833%   $75.936   $75.94   $75.95   $75.90  
  Purchase #4 $63.53   4.261%   $66.237   $66.24   $66.25   $66.20  
  Purchase #5 $88.39   4.532%   $92.3958   $92.40   $92.40   $92.40  
  Purchase #6 $113.65   9.196%   $124.1013   $124.10   $124.10   $124.10  
  Purchase #7 $232.46   12.474%   $261.4571   $261.46   $261.45   $261.50  
  7 purchase totals = $859.29       $945.2430   $945.26   $945.30   $945.20