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 $24.83   3.626%   $25.7303   $25.73   $25.75   $25.70  
  Purchase #2 $215.68   7.826%   $232.5591   $232.56   $232.55   $232.60  
  Purchase #3 $87.73   12.382%   $98.5927   $98.59   $98.60   $98.60  
  Purchase #4 $187.44   5.265%   $197.3087   $197.31   $197.30   $197.30  
  Purchase #5 $195.46   13.828%   $222.4882   $222.49   $222.50   $222.50  
  Purchase #6 $77.53   9.269%   $84.7163   $84.72   $84.70   $84.70  
  Purchase #7 $68.88   8.373%   $74.6473   $74.65   $74.65   $74.60  
  7 purchase totals = $857.55       $936.0426   $936.05   $936.05   $936.00