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 $66.82   12.201%   $74.9727   $74.97   $74.95   $75.00  
  Purchase #2 $249.91   10.291%   $275.6282   $275.63   $275.65   $275.60  
  Purchase #3 $206.86   5.717%   $218.6862   $218.69   $218.70   $218.70  
  Purchase #4 $94.44   4.595%   $98.7795   $98.78   $98.80   $98.80  
  Purchase #5 $88.45   12.223%   $99.2612   $99.26   $99.25   $99.30  
  Purchase #6 $64.96   7.559%   $69.8703   $69.87   $69.85   $69.90  
  Purchase #7 $100.70   6.485%   $107.2304   $107.23   $107.25   $107.20  
  7 purchase totals = $872.14       $944.4285   $944.43   $944.45   $944.50