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 $72.88   13.311%   $82.5811   $82.58   $82.60   $82.60  
  Purchase #2 $47.28   11.853%   $52.8841   $52.88   $52.90   $52.90  
  Purchase #3 $81.53   7.302%   $87.4833   $87.48   $87.50   $87.50  
  Purchase #4 $49.25   6.324%   $52.3646   $52.36   $52.35   $52.40  
  Purchase #5 $6.48   6.491%   $6.9006   $6.90   $6.90   $6.90  
  Purchase #6 $214.60   8.321%   $232.4569   $232.46   $232.45   $232.50  
  Purchase #7 $202.39   8.318%   $219.2248   $219.22   $219.20   $219.20  
  7 purchase totals = $674.41       $733.8954   $733.88   $733.90   $734.00