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 $192.61   10.732%   $213.2809   $213.28   $213.30   $213.30  
  Purchase #2 $183.39   4.519%   $191.6774   $191.68   $191.70   $191.70  
  Purchase #3 $119.54   6.195%   $126.9455   $126.95   $126.95   $126.90  
  Purchase #4 $177.39   12.284%   $199.1806   $199.18   $199.20   $199.20  
  Purchase #5 $168.75   6.813%   $180.2469   $180.25   $180.25   $180.20  
  Purchase #6 $244.25   7.311%   $262.1071   $262.11   $262.10   $262.10  
  Purchase #7 $139.62   10.623%   $154.4518   $154.45   $154.45   $154.50  
  7 purchase totals = $1,225.55       $1,327.8902   $1,327.90   $1,327.95   $1,327.90