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 $118.85   13.738%   $135.1776   $135.18   $135.20   $135.20  
  Purchase #2 $203.39   11.825%   $227.4409   $227.44   $227.45   $227.40  
  Purchase #3 $96.77   5.714%   $102.2994   $102.30   $102.30   $102.30  
  Purchase #4 $169.42   11.322%   $188.6017   $188.60   $188.60   $188.60  
  Purchase #5 $69.29   11.548%   $77.2916   $77.29   $77.30   $77.30  
  Purchase #6 $227.34   5.445%   $239.7187   $239.72   $239.70   $239.70  
  Purchase #7 $88.57   4.556%   $92.6052   $92.61   $92.60   $92.60  
  7 purchase totals = $973.63       $1,063.1351   $1,063.14   $1,063.15   $1,063.10