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 $240.70   11.361%   $268.0459   $268.05   $268.05   $268.00  
  Purchase #2 $117.71   10.393%   $129.9436   $129.94   $129.95   $129.90  
  Purchase #3 $158.26   10.569%   $174.9865   $174.99   $175.00   $175.00  
  Purchase #4 $202.87   5.861%   $214.7602   $214.76   $214.75   $214.80  
  Purchase #5 $154.67   5.282%   $162.8397   $162.84   $162.85   $162.80  
  Purchase #6 $230.71   7.145%   $247.1942   $247.19   $247.20   $247.20  
  Purchase #7 $112.75   9.373%   $123.3181   $123.32   $123.30   $123.30  
  7 purchase totals = $1,217.67       $1,321.0882   $1,321.09   $1,321.10   $1,321.00