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 $202.28   8.559%   $219.5931   $219.59   $219.60   $219.60  
  Purchase #2 $138.91   10.841%   $153.9692   $153.97   $153.95   $154.00  
  Purchase #3 $66.91   9.335%   $73.156   $73.16   $73.15   $73.20  
  Purchase #4 $125.73   5.197%   $132.2642   $132.26   $132.25   $132.30  
  Purchase #5 $45.87   5.309%   $48.3052   $48.31   $48.30   $48.30  
  Purchase #6 $112.75   4.238%   $117.5283   $117.53   $117.55   $117.50  
  Purchase #7 $184.86   13.784%   $210.3411   $210.34   $210.35   $210.30  
  7 purchase totals = $877.31       $955.1571   $955.16   $955.15   $955.20