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 $57.57   10.224%   $63.456   $63.46   $63.45   $63.50  
  Purchase #2 $229.67   13.373%   $260.3838   $260.38   $260.40   $260.40  
  Purchase #3 $153.79   3.619%   $159.3557   $159.36   $159.35   $159.40  
  Purchase #4 $105.34   13.781%   $119.8569   $119.86   $119.85   $119.90  
  Purchase #5 $41.48   7.219%   $44.4744   $44.47   $44.45   $44.50  
  Purchase #6 $96.56   5.189%   $101.5705   $101.57   $101.55   $101.60  
  Purchase #7 $165.42   6.374%   $175.9639   $175.96   $175.95   $176.00  
  7 purchase totals = $849.83       $925.0612   $925.06   $925.00   $925.30