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 $22.42   12.724%   $25.2727   $25.27   $25.25   $25.30  
  Purchase #2 $232.55   12.746%   $262.1908   $262.19   $262.20   $262.20  
  Purchase #3 $62.90   5.261%   $66.2092   $66.21   $66.20   $66.20  
  Purchase #4 $228.40   8.552%   $247.9328   $247.93   $247.95   $247.90  
  Purchase #5 $133.46   13.866%   $151.9656   $151.97   $151.95   $152.00  
  Purchase #6 $92.49   6.862%   $98.8367   $98.84   $98.85   $98.80  
  Purchase #7 $95.74   8.618%   $103.9909   $103.99   $104.00   $104.00  
  7 purchase totals = $867.96       $956.3987   $956.40   $956.40   $956.40