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 $228.96   11.678%   $255.6979   $255.70   $255.70   $255.70  
  Purchase #2 $171.31   12.295%   $192.3726   $192.37   $192.35   $192.40  
  Purchase #3 $123.68   4.513%   $129.2617   $129.26   $129.25   $129.30  
  Purchase #4 $110.45   3.176%   $113.9579   $113.96   $113.95   $114.00  
  Purchase #5 $108.99   5.827%   $115.3408   $115.34   $115.35   $115.30  
  Purchase #6 $235.66   6.507%   $250.9944   $250.99   $251.00   $251.00  
  Purchase #7 $215.69   13.332%   $244.4458   $244.45   $244.45   $244.40  
  7 purchase totals = $1,194.74       $1,302.0711   $1,302.07   $1,302.05   $1,302.10