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 $194.38   11.762%   $217.243   $217.24   $217.25   $217.20  
  Purchase #2 $241.88   13.111%   $273.5929   $273.59   $273.60   $273.60  
  Purchase #3 $108.77   6.103%   $115.4082   $115.41   $115.40   $115.40  
  Purchase #4 $95.84   3.236%   $98.9414   $98.94   $98.95   $98.90  
  Purchase #5 $85.67   8.154%   $92.6555   $92.66   $92.65   $92.70  
  Purchase #6 $204.44   7.236%   $219.2333   $219.23   $219.25   $219.20  
  Purchase #7 $110.33   13.446%   $125.165   $125.17   $125.15   $125.20  
  7 purchase totals = $1,041.31       $1,142.2393   $1,142.24   $1,142.25   $1,142.20