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 $208.94   8.635%   $226.982   $226.98   $227.00   $227.00  
  Purchase #2 $112.30   11.487%   $125.1999   $125.20   $125.20   $125.20  
  Purchase #3 $71.83   6.161%   $76.2554   $76.26   $76.25   $76.30  
  Purchase #4 $148.71   5.276%   $156.5559   $156.56   $156.55   $156.60  
  Purchase #5 $5.46   13.296%   $6.186   $6.19   $6.20   $6.20  
  Purchase #6 $17.83   10.424%   $19.6886   $19.69   $19.70   $19.70  
  Purchase #7 $44.89   4.810%   $47.0492   $47.05   $47.05   $47.00  
  7 purchase totals = $609.96       $657.9170   $657.93   $657.95   $658.00