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	$81.53	12.144%	$91.431	$91.43	$91.45	$91.40
Purchase #2	$10.53	4.697%	$11.0246	$11.02	$11.00	$11.00
Purchase #3	$83.52	6.129%	$88.6389	$88.64	$88.65	$88.60
Purchase #4	$125.66	3.773%	$130.4012	$130.40	$130.40	$130.40
Purchase #5	$148.82	7.760%	$160.3684	$160.37	$160.35	$160.40
Purchase #6	$54.50	5.545%	$57.522	$57.52	$57.50	$57.50
Purchase #7	$79.94	6.526%	$85.1569	$85.16	$85.15	$85.20
7 purchase totals =	$584.50		$624.5430	$624.54	$624.50	$624.50