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	$79.94	10.819%	$88.5887	$88.59	$88.60	$88.60
Purchase #2	$159.25	9.204%	$173.9074	$173.91	$173.90	$173.90
Purchase #3	$51.48	13.160%	$58.2548	$58.25	$58.25	$58.30
Purchase #4	$144.63	4.806%	$151.5809	$151.58	$151.60	$151.60
Purchase #5	$53.40	10.719%	$59.1239	$59.12	$59.10	$59.10
Purchase #6	$26.38	7.701%	$28.4115	$28.41	$28.40	$28.40
Purchase #7	$203.81	7.654%	$219.4096	$219.41	$219.40	$219.40
7 purchase totals =	$718.89		$779.2768	$779.27	$779.25	$779.30