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	$110.74	4.318%	$115.5218	$115.52	$115.50	$115.50
Purchase #2	$152.84	13.109%	$172.8758	$172.88	$172.90	$172.90
Purchase #3	$146.25	13.139%	$165.4658	$165.47	$165.45	$165.50
Purchase #4	$59.58	5.482%	$62.8462	$62.85	$62.85	$62.80
Purchase #5	$185.62	6.297%	$197.3085	$197.31	$197.30	$197.30
Purchase #6	$68.52	8.212%	$74.1469	$74.15	$74.15	$74.10
Purchase #7	$103.71	5.576%	$109.4929	$109.49	$109.50	$109.50
7 purchase totals =	$827.26		$897.6579	$897.67	$897.65	$897.60