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	$81.25	11.148%	$90.3078	$90.31	$90.30	$90.30
Purchase #2	$214.95	7.362%	$230.7746	$230.77	$230.75	$230.80
Purchase #3	$56.66	6.206%	$60.1763	$60.18	$60.20	$60.20
Purchase #4	$39.30	10.693%	$43.5023	$43.50	$43.50	$43.50
Purchase #5	$74.86	4.323%	$78.0962	$78.10	$78.10	$78.10
Purchase #6	$155.64	9.796%	$170.8865	$170.89	$170.90	$170.90
Purchase #7	$37.30	6.692%	$39.7961	$39.80	$39.80	$39.80
7 purchase totals =	$659.96		$713.5398	$713.55	$713.55	$713.60