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 $114.43   3.350%   $118.2634   $118.26   $118.25   $118.30  
  Purchase #2 $226.68   7.541%   $243.7739   $243.77   $243.75   $243.80  
  Purchase #3 $239.37   5.494%   $252.521   $252.52   $252.50   $252.50  
  Purchase #4 $176.39   10.244%   $194.4594   $194.46   $194.45   $194.50  
  Purchase #5 $188.48   9.546%   $206.4723   $206.47   $206.45   $206.50  
  Purchase #6 $127.55   7.744%   $137.4275   $137.43   $137.45   $137.40  
  Purchase #7 $98.87   11.554%   $110.2934   $110.29   $110.30   $110.30  
  7 purchase totals = $1,171.77       $1,263.2109   $1,263.20   $1,263.15   $1,263.30