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 $84.54   12.324%   $94.9587   $94.96   $94.95   $95.00  
  Purchase #2 $111.88   11.668%   $124.9342   $124.93   $124.95   $124.90  
  Purchase #3 $226.91   7.137%   $243.1046   $243.10   $243.10   $243.10  
  Purchase #4 $47.30   5.637%   $49.9663   $49.97   $49.95   $50.00  
  Purchase #5 $114.78   13.515%   $130.2925   $130.29   $130.30   $130.30  
  Purchase #6 $98.91   3.253%   $102.1275   $102.13   $102.15   $102.10  
  Purchase #7 $103.93   6.178%   $110.3508   $110.35   $110.35   $110.40  
  7 purchase totals = $788.25       $855.7346   $855.73   $855.75   $855.80