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 $42.82   12.426%   $48.1408   $48.14   $48.15   $48.10  
  Purchase #2 $217.56   7.685%   $234.2795   $234.28   $234.30   $234.30  
  Purchase #3 $151.94   4.639%   $158.9885   $158.99   $159.00   $159.00  
  Purchase #4 $50.74   13.587%   $57.634   $57.63   $57.65   $57.60  
  Purchase #5 $86.27   5.814%   $91.2857   $91.29   $91.30   $91.30  
  Purchase #6 $112.61   6.208%   $119.6008   $119.60   $119.60   $119.60  
  Purchase #7 $171.39   6.796%   $183.0377   $183.04   $183.05   $183.00  
  7 purchase totals = $833.33       $892.9670   $892.97   $893.05   $892.90