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 $112.78   4.562%   $117.925   $117.93   $117.95   $117.90  
  Purchase #2 $79.77   8.511%   $86.5592   $86.56   $86.55   $86.60  
  Purchase #3 $79.92   11.308%   $88.9574   $88.96   $88.95   $89.00  
  Purchase #4 $9.61   13.346%   $10.8926   $10.89   $10.90   $10.90  
  Purchase #5 $114.38   3.867%   $118.8031   $118.80   $118.80   $118.80  
  Purchase #6 $50.33   9.624%   $55.1738   $55.17   $55.15   $55.20  
  Purchase #7 $188.84   10.788%   $209.2121   $209.21   $209.20   $209.20  
  7 purchase totals = $635.63       $687.5232   $687.52   $687.50   $687.60