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 $84.42   13.211%   $95.5727   $95.57   $95.55   $95.60  
  Purchase #2 $104.47   13.454%   $118.5254   $118.53   $118.55   $118.50  
  Purchase #3 $27.26   9.671%   $29.8963   $29.90   $29.90   $29.90  
  Purchase #4 $223.49   8.480%   $242.442   $242.44   $242.45   $242.40  
  Purchase #5 $87.39   6.130%   $92.747   $92.75   $92.75   $92.70  
  Purchase #6 $29.89   11.449%   $33.3121   $33.31   $33.30   $33.30  
  Purchase #7 $193.39   6.145%   $205.2738   $205.27   $205.25   $205.30  
  7 purchase totals = $750.31       $817.7693   $817.77   $817.75   $817.70