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 $112.53   4.352%   $117.4273   $117.43   $117.45   $117.40  
  Purchase #2 $200.41   6.159%   $212.7533   $212.75   $212.75   $212.80  
  Purchase #3 $34.72   3.435%   $35.9126   $35.91   $35.90   $35.90  
  Purchase #4 $114.78   10.390%   $126.7056   $126.71   $126.70   $126.70  
  Purchase #5 $115.71   12.240%   $129.8729   $129.87   $129.85   $129.90  
  Purchase #6 $44.80   4.482%   $46.8079   $46.81   $46.80   $46.80  
  Purchase #7 $96.93   7.457%   $104.1581   $104.16   $104.15   $104.20  
  7 purchase totals = $719.88       $773.6377   $773.64   $773.60   $773.70