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 $51.81   7.795%   $55.8486   $55.85   $55.85   $55.80  
  Purchase #2 $196.82   8.547%   $213.6422   $213.64   $213.65   $213.60  
  Purchase #3 $66.54   5.656%   $70.3035   $70.30   $70.30   $70.30  
  Purchase #4 $125.85   4.291%   $131.2502   $131.25   $131.25   $131.30  
  Purchase #5 $24.48   4.294%   $25.5312   $25.53   $25.55   $25.50  
  Purchase #6 $43.47   10.758%   $48.1465   $48.15   $48.15   $48.10  
  Purchase #7 $216.32   9.256%   $236.3426   $236.34   $236.35   $236.30  
  7 purchase totals = $725.29       $781.0648   $781.06   $781.10   $780.90