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 $48.63   11.458%   $54.202   $54.20   $54.20   $54.20  
  Purchase #2 $204.36   10.682%   $226.1897   $226.19   $226.20   $226.20  
  Purchase #3 $44.69   13.303%   $50.6351   $50.64   $50.65   $50.60  
  Purchase #4 $79.48   4.856%   $83.3395   $83.34   $83.35   $83.30  
  Purchase #5 $202.90   13.189%   $229.6605   $229.66   $229.65   $229.70  
  Purchase #6 $111.48   11.241%   $124.0115   $124.01   $124.00   $124.00  
  Purchase #7 $187.56   10.872%   $207.9515   $207.95   $207.95   $208.00  
  7 purchase totals = $879.10       $975.9898   $975.99   $976.00   $976.00