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 $52.43   3.330%   $54.1759   $54.18   $54.20   $54.20  
  Purchase #2 $228.91   3.226%   $236.2946   $236.29   $236.30   $236.30  
  Purchase #3 $178.35   8.318%   $193.1852   $193.19   $193.20   $193.20  
  Purchase #4 $19.95   13.246%   $22.5926   $22.59   $22.60   $22.60  
  Purchase #5 $86.53   6.795%   $92.4097   $92.41   $92.40   $92.40  
  Purchase #6 $217.50   8.413%   $235.7983   $235.80   $235.80   $235.80  
  Purchase #7 $146.63   7.314%   $157.3545   $157.35   $157.35   $157.40  
  7 purchase totals = $930.30       $991.8108   $991.81   $991.85   $991.90