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 $231.97   7.765%   $249.9825   $249.98   $250.00   $250.00  
  Purchase #2 $150.49   4.492%   $157.25   $157.25   $157.25   $157.30  
  Purchase #3 $132.75   7.368%   $142.531   $142.53   $142.55   $142.50  
  Purchase #4 $200.73   6.850%   $214.48   $214.48   $214.50   $214.50  
  Purchase #5 $218.77   11.621%   $244.1933   $244.19   $244.20   $244.20  
  Purchase #6 $184.30   6.846%   $196.9172   $196.92   $196.90   $196.90  
  Purchase #7 $153.92   12.313%   $172.8722   $172.87   $172.85   $172.90  
  7 purchase totals = $1,272.93       $1,378.2262   $1,378.22   $1,378.25   $1,378.30