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 $233.47   12.747%   $263.2304   $263.23   $263.25   $263.20  
  Purchase #2 $159.87   9.427%   $174.9409   $174.94   $174.95   $174.90  
  Purchase #3 $43.75   12.661%   $49.2892   $49.29   $49.30   $49.30  
  Purchase #4 $5.40   6.389%   $5.745   $5.75   $5.75   $5.70  
  Purchase #5 $126.68   10.213%   $139.6178   $139.62   $139.60   $139.60  
  Purchase #6 $157.37   3.249%   $162.483   $162.48   $162.50   $162.50  
  Purchase #7 $14.69   9.499%   $16.0854   $16.09   $16.10   $16.10  
  7 purchase totals = $741.23       $811.3917   $811.40   $811.45   $811.30