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 $89.48   4.161%   $93.2033   $93.20   $93.20   $93.20  
  Purchase #2 $195.77   11.287%   $217.8666   $217.87   $217.85   $217.90  
  Purchase #3 $118.47   3.599%   $122.7337   $122.73   $122.75   $122.70  
  Purchase #4 $109.50   9.249%   $119.6277   $119.63   $119.65   $119.60  
  Purchase #5 $45.66   9.138%   $49.8324   $49.83   $49.85   $49.80  
  Purchase #6 $54.95   5.491%   $57.9673   $57.97   $57.95   $58.00  
  Purchase #7 $44.84   4.297%   $46.7668   $46.77   $46.75   $46.80  
  7 purchase totals = $658.67       $707.9978   $708.00   $708.00   $708.00