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	$77.85	3.415%	$80.5086	$80.51	$80.50	$80.50
Purchase #2	$161.81	8.842%	$176.1172	$176.12	$176.10	$176.10
Purchase #3	$111.77	3.616%	$115.8116	$115.81	$115.80	$115.80
Purchase #4	$172.37	4.150%	$179.5234	$179.52	$179.50	$179.50
Purchase #5	$10.42	13.817%	$11.8597	$11.86	$11.85	$11.90
Purchase #6	$170.29	5.872%	$180.2894	$180.29	$180.30	$180.30
Purchase #7	$72.82	5.204%	$76.6096	$76.61	$76.60	$76.60
7 purchase totals =	$777.33		$820.7195	$820.72	$820.65	$820.70