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 $201.77   5.197%   $212.256   $212.26   $212.25   $212.30  
  Purchase #2 $33.25   13.463%   $37.7264   $37.73   $37.75   $37.70  
  Purchase #3 $186.66   10.318%   $205.9196   $205.92   $205.90   $205.90  
  Purchase #4 $195.77   9.853%   $215.0592   $215.06   $215.05   $215.10  
  Purchase #5 $223.45   4.205%   $232.8461   $232.85   $232.85   $232.80  
  Purchase #6 $241.56   5.733%   $255.4086   $255.41   $255.40   $255.40  
  Purchase #7 $98.53   8.825%   $107.2253   $107.23   $107.25   $107.20  
  7 purchase totals = $1,180.99       $1,266.4412   $1,266.46   $1,266.45   $1,266.40