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	$246.32	9.831%	$270.5357	$270.54	$270.55	$270.50
Purchase #2	$26.36	11.844%	$29.4821	$29.48	$29.50	$29.50
Purchase #3	$71.93	13.831%	$81.8786	$81.88	$81.90	$81.90
Purchase #4	$77.72	10.439%	$85.8332	$85.83	$85.85	$85.80
Purchase #5	$192.66	6.511%	$205.2041	$205.20	$205.20	$205.20
Purchase #6	$35.73	6.187%	$37.9406	$37.94	$37.95	$37.90
Purchase #7	$9.81	11.183%	$10.9071	$10.91	$10.90	$10.90
7 purchase totals =	$660.53		$721.7814	$721.78	$721.85	$721.70