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	$47.47	13.491%	$53.8742	$53.87	$53.85	$53.90
Purchase #2	$143.80	3.308%	$148.5569	$148.56	$148.55	$148.60
Purchase #3	$25.58	11.659%	$28.5624	$28.56	$28.55	$28.60
Purchase #4	$162.52	5.180%	$170.9385	$170.94	$170.95	$170.90
Purchase #5	$33.67	12.523%	$37.8865	$37.89	$37.90	$37.90
Purchase #6	$13.46	7.554%	$14.4768	$14.48	$14.50	$14.50
Purchase #7	$60.32	13.495%	$68.4602	$68.46	$68.45	$68.50
7 purchase totals =	$486.82		$522.7555	$522.76	$522.75	$522.90