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 $83.81   10.511%   $92.6193   $92.62   $92.60   $92.60  
  Purchase #2 $238.40   5.809%   $252.2487   $252.25   $252.25   $252.20  
  Purchase #3 $32.55   4.258%   $33.936   $33.94   $33.95   $33.90  
  Purchase #4 $128.35   3.831%   $133.2671   $133.27   $133.25   $133.30  
  Purchase #5 $20.43   10.138%   $22.5012   $22.50   $22.50   $22.50  
  Purchase #6 $182.69   13.608%   $207.5505   $207.55   $207.55   $207.60  
  Purchase #7 $151.83   12.741%   $171.1747   $171.17   $171.15   $171.20  
  7 purchase totals = $838.06       $913.2975   $913.30   $913.25   $913.30