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 $214.56   13.863%   $244.3045   $244.30   $244.30   $244.30  
  Purchase #2 $158.99   13.546%   $180.5268   $180.53   $180.55   $180.50  
  Purchase #3 $206.60   8.623%   $224.4151   $224.42   $224.40   $224.40  
  Purchase #4 $73.65   12.588%   $82.9211   $82.92   $82.90   $82.90  
  Purchase #5 $186.70   8.463%   $202.5004   $202.50   $202.50   $202.50  
  Purchase #6 $34.41   3.558%   $35.6343   $35.63   $35.65   $35.60  
  Purchase #7 $93.43   10.515%   $103.2542   $103.25   $103.25   $103.30  
  7 purchase totals = $968.34       $1,073.5564   $1,073.55   $1,073.55   $1,073.50