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 $114.37   13.218%   $129.4874   $129.49   $129.50   $129.50  
  Purchase #2 $83.72   11.441%   $93.2984   $93.30   $93.30   $93.30  
  Purchase #3 $204.61   11.356%   $227.8455   $227.85   $227.85   $227.80  
  Purchase #4 $11.52   5.585%   $12.1634   $12.16   $12.15   $12.20  
  Purchase #5 $104.63   9.827%   $114.912   $114.91   $114.90   $114.90  
  Purchase #6 $78.38   3.187%   $80.878   $80.88   $80.90   $80.90  
  Purchase #7 $97.56   7.660%   $105.0331   $105.03   $105.05   $105.00  
  7 purchase totals = $694.79       $763.6178   $763.62   $763.65   $763.60