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 $66.27   10.635%   $73.3178   $73.32   $73.30   $73.30  
  Purchase #2 $131.76   9.796%   $144.6672   $144.67   $144.65   $144.70  
  Purchase #3 $80.56   13.201%   $91.1947   $91.19   $91.20   $91.20  
  Purchase #4 $132.82   13.618%   $150.9074   $150.91   $150.90   $150.90  
  Purchase #5 $134.51   4.354%   $140.3666   $140.37   $140.35   $140.40  
  Purchase #6 $61.63   13.427%   $69.9051   $69.91   $69.90   $69.90  
  Purchase #7 $191.87   11.346%   $213.6396   $213.64   $213.65   $213.60  
  7 purchase totals = $799.42       $883.9984   $884.01   $883.95   $884.00