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 $150.96   8.142%   $163.2512   $163.25   $163.25   $163.30  
  Purchase #2 $78.80   3.251%   $81.3618   $81.36   $81.35   $81.40  
  Purchase #3 $168.80   5.489%   $178.0654   $178.07   $178.05   $178.10  
  Purchase #4 $79.76   8.806%   $86.7837   $86.78   $86.80   $86.80  
  Purchase #5 $100.93   13.263%   $114.3163   $114.32   $114.30   $114.30  
  Purchase #6 $118.54   6.196%   $125.8847   $125.88   $125.90   $125.90  
  Purchase #7 $248.30   3.726%   $257.5517   $257.55   $257.55   $257.60  
  7 purchase totals = $946.09       $1,007.2148   $1,007.21   $1,007.20   $1,007.40