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 $127.42   6.696%   $135.952   $135.95   $135.95   $136.00  
  Purchase #2 $179.87   6.135%   $190.905   $190.91   $190.90   $190.90  
  Purchase #3 $227.88   4.713%   $238.62   $238.62   $238.60   $238.60  
  Purchase #4 $170.53   3.868%   $177.1261   $177.13   $177.15   $177.10  
  Purchase #5 $114.97   10.252%   $126.7567   $126.76   $126.75   $126.80  
  Purchase #6 $185.91   6.107%   $197.2635   $197.26   $197.25   $197.30  
  Purchase #7 $136.90   10.312%   $151.0171   $151.02   $151.00   $151.00  
  7 purchase totals = $1,143.48       $1,217.6404   $1,217.65   $1,217.60   $1,217.70