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 $37.72   9.778%   $41.4083   $41.41   $41.40   $41.40  
  Purchase #2 $104.61   12.152%   $117.3222   $117.32   $117.30   $117.30  
  Purchase #3 $117.92   8.736%   $128.2215   $128.22   $128.20   $128.20  
  Purchase #4 $233.34   9.676%   $255.918   $255.92   $255.90   $255.90  
  Purchase #5 $172.26   13.315%   $195.1964   $195.20   $195.20   $195.20  
  Purchase #6 $186.49   3.692%   $193.3752   $193.38   $193.40   $193.40  
  Purchase #7 $227.68   7.217%   $244.1117   $244.11   $244.10   $244.10  
  7 purchase totals = $1,080.02       $1,175.5533   $1,175.56   $1,175.50   $1,175.50