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	$40.74	12.603%	$45.8745	$45.87	$45.85	$45.90
Purchase #2	$173.71	6.685%	$185.3225	$185.32	$185.30	$185.30
Purchase #3	$91.33	13.800%	$103.9335	$103.93	$103.95	$103.90
Purchase #4	$180.37	6.840%	$192.7073	$192.71	$192.70	$192.70
Purchase #5	$46.28	9.492%	$50.6729	$50.67	$50.65	$50.70
Purchase #6	$86.60	5.563%	$91.4176	$91.42	$91.40	$91.40
Purchase #7	$207.91	5.269%	$218.8648	$218.86	$218.85	$218.90
7 purchase totals =	$826.94		$888.7931	$888.78	$888.70	$888.80