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 $93.61   10.248%   $103.2032   $103.20   $103.20   $103.20  
  Purchase #2 $104.39   8.837%   $113.6149   $113.61   $113.60   $113.60  
  Purchase #3 $209.25   7.185%   $224.2846   $224.28   $224.30   $224.30  
  Purchase #4 $22.29   13.592%   $25.3197   $25.32   $25.30   $25.30  
  Purchase #5 $62.32   5.702%   $65.8735   $65.87   $65.85   $65.90  
  Purchase #6 $114.30   9.707%   $125.3951   $125.40   $125.40   $125.40  
  Purchase #7 $114.61   9.548%   $125.553   $125.55   $125.55   $125.60  
  7 purchase totals = $720.77       $783.2440   $783.23   $783.20   $783.30