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 $47.51   3.459%   $49.1534   $49.15   $49.15   $49.20  
  Purchase #2 $244.78   5.342%   $257.8561   $257.86   $257.85   $257.90  
  Purchase #3 $46.28   3.328%   $47.8202   $47.82   $47.80   $47.80  
  Purchase #4 $79.33   3.263%   $81.9185   $81.92   $81.90   $81.90  
  Purchase #5 $207.49   5.267%   $218.4185   $218.42   $218.40   $218.40  
  Purchase #6 $182.63   8.301%   $197.7901   $197.79   $197.80   $197.80  
  Purchase #7 $13.54   4.332%   $14.1266   $14.13   $14.15   $14.10  
  7 purchase totals = $821.56       $867.0834   $867.09   $867.05   $867.10