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 $164.71   10.766%   $182.4427   $182.44   $182.45   $182.40  
  Purchase #2 $238.98   12.377%   $268.5586   $268.56   $268.55   $268.60  
  Purchase #3 $8.46   4.361%   $8.8289   $8.83   $8.85   $8.80  
  Purchase #4 $164.41   8.234%   $177.9475   $177.95   $177.95   $177.90  
  Purchase #5 $224.77   5.636%   $237.438   $237.44   $237.45   $237.40  
  Purchase #6 $109.32   11.698%   $122.1083   $122.11   $122.10   $122.10  
  Purchase #7 $200.36   7.513%   $215.413   $215.41   $215.40   $215.40  
  7 purchase totals = $1,111.01       $1,212.7370   $1,212.74   $1,212.75   $1,212.60