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 $80.99   5.266%   $85.2549   $85.25   $85.25   $85.30  
  Purchase #2 $107.98   4.257%   $112.5767   $112.58   $112.60   $112.60  
  Purchase #3 $204.76   4.548%   $214.0725   $214.07   $214.05   $214.10  
  Purchase #4 $34.37   6.797%   $36.7061   $36.71   $36.70   $36.70  
  Purchase #5 $173.96   4.215%   $181.2924   $181.29   $181.30   $181.30  
  Purchase #6 $114.44   7.839%   $123.411   $123.41   $123.40   $123.40  
  Purchase #7 $58.42   10.857%   $64.7627   $64.76   $64.75   $64.80  
  7 purchase totals = $774.92       $818.0763   $818.07   $818.05   $818.20