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 $213.54   6.746%   $227.9454   $227.95   $227.95   $227.90  
  Purchase #2 $176.80   10.576%   $195.4984   $195.50   $195.50   $195.50  
  Purchase #3 $32.64   9.578%   $35.7663   $35.77   $35.75   $35.80  
  Purchase #4 $125.58   11.832%   $140.4386   $140.44   $140.45   $140.40  
  Purchase #5 $163.63   7.171%   $175.3639   $175.36   $175.35   $175.40  
  Purchase #6 $16.78   12.702%   $18.9114   $18.91   $18.90   $18.90  
  Purchase #7 $215.71   8.342%   $233.7045   $233.70   $233.70   $233.70  
  7 purchase totals = $944.68       $1,027.6285   $1,027.63   $1,027.60   $1,027.60