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 $62.71   3.659%   $65.0046   $65.00   $65.00   $65.00  
  Purchase #2 $32.83   6.491%   $34.961   $34.96   $34.95   $35.00  
  Purchase #3 $233.72   12.173%   $262.1707   $262.17   $262.15   $262.20  
  Purchase #4 $198.36   9.306%   $216.8194   $216.82   $216.80   $216.80  
  Purchase #5 $242.87   12.504%   $273.2385   $273.24   $273.25   $273.20  
  Purchase #6 $200.74   8.756%   $218.3168   $218.32   $218.30   $218.30  
  Purchase #7 $162.57   13.863%   $185.1071   $185.11   $185.10   $185.10  
  7 purchase totals = $1,133.80       $1,255.6181   $1,255.62   $1,255.55   $1,255.60