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 $104.58   9.491%   $114.5057   $114.51   $114.50   $114.50  
  Purchase #2 $97.78   3.628%   $101.3275   $101.33   $101.35   $101.30  
  Purchase #3 $25.42   5.551%   $26.8311   $26.83   $26.85   $26.80  
  Purchase #4 $118.34   7.277%   $126.9516   $126.95   $126.95   $127.00  
  Purchase #5 $242.62   12.474%   $272.8844   $272.88   $272.90   $272.90  
  Purchase #6 $108.32   12.394%   $121.7452   $121.75   $121.75   $121.70  
  Purchase #7 $190.96   4.801%   $200.128   $200.13   $200.15   $200.10  
  7 purchase totals = $888.02       $964.3735   $964.38   $964.45   $964.30