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	$103.68	10.597%	$114.667	$114.67	$114.65	$114.70
Purchase #2	$99.45	12.766%	$112.1458	$112.15	$112.15	$112.10
Purchase #3	$17.89	4.404%	$18.6779	$18.68	$18.70	$18.70
Purchase #4	$37.53	7.329%	$40.2806	$40.28	$40.30	$40.30
Purchase #5	$204.50	8.714%	$222.3201	$222.32	$222.30	$222.30
Purchase #6	$8.58	10.813%	$9.5078	$9.51	$9.50	$9.50
Purchase #7	$118.76	10.430%	$131.1467	$131.15	$131.15	$131.10
7 purchase totals =	$590.39		$648.7459	$648.76	$648.75	$648.70