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 $248.46   9.588%   $272.2823   $272.28   $272.30   $272.30  
  Purchase #2 $236.98   3.308%   $244.8193   $244.82   $244.80   $244.80  
  Purchase #3 $96.96   7.598%   $104.327   $104.33   $104.35   $104.30  
  Purchase #4 $117.38   10.291%   $129.4596   $129.46   $129.45   $129.50  
  Purchase #5 $18.80   8.350%   $20.3698   $20.37   $20.35   $20.40  
  Purchase #6 $114.56   8.558%   $124.364   $124.36   $124.35   $124.40  
  Purchase #7 $52.32   3.291%   $54.0419   $54.04   $54.05   $54.00  
  7 purchase totals = $885.46       $949.6639   $949.66   $949.65   $949.70