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 $118.91   5.535%   $125.4917   $125.49   $125.50   $125.50  
  Purchase #2 $22.97   5.632%   $24.2637   $24.26   $24.25   $24.30  
  Purchase #3 $211.73   6.447%   $225.3802   $225.38   $225.40   $225.40  
  Purchase #4 $47.35   3.756%   $49.1285   $49.13   $49.15   $49.10  
  Purchase #5 $67.77   8.560%   $73.5711   $73.57   $73.55   $73.60  
  Purchase #6 $151.75   13.265%   $171.8796   $171.88   $171.90   $171.90  
  Purchase #7 $192.51   5.811%   $203.6968   $203.70   $203.70   $203.70  
  7 purchase totals = $812.99       $873.4116   $873.41   $873.45   $873.50