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 $112.54   10.469%   $124.3218   $124.32   $124.30   $124.30  
  Purchase #2 $14.70   3.413%   $15.2017   $15.20   $15.20   $15.20  
  Purchase #3 $160.36   6.810%   $171.2805   $171.28   $171.30   $171.30  
  Purchase #4 $211.40   6.209%   $224.5258   $224.53   $224.55   $224.50  
  Purchase #5 $127.64   7.725%   $137.5002   $137.50   $137.50   $137.50  
  Purchase #6 $43.47   13.423%   $49.305   $49.31   $49.30   $49.30  
  Purchase #7 $81.90   12.828%   $92.4061   $92.41   $92.40   $92.40  
  7 purchase totals = $752.01       $814.5411   $814.55   $814.55   $814.50