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 $85.98   10.832%   $95.2934   $95.29   $95.30   $95.30  
  Purchase #2 $44.29   3.697%   $45.9274   $45.93   $45.95   $45.90  
  Purchase #3 $77.35   5.376%   $81.5083   $81.51   $81.50   $81.50  
  Purchase #4 $119.83   11.342%   $133.4211   $133.42   $133.40   $133.40  
  Purchase #5 $91.64   8.190%   $99.1453   $99.15   $99.15   $99.10  
  Purchase #6 $241.36   8.235%   $261.236   $261.24   $261.25   $261.20  
  Purchase #7 $195.91   12.513%   $220.4242   $220.42   $220.40   $220.40  
  7 purchase totals = $856.36       $936.9557   $936.96   $936.95   $936.80