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	$250.46	11.249%	$278.6342	$278.63	$278.65	$278.60
Purchase #2	$131.91	9.432%	$144.3518	$144.35	$144.35	$144.40
Purchase #3	$70.50	10.424%	$77.8489	$77.85	$77.85	$77.80
Purchase #4	$10.83	13.114%	$12.2502	$12.25	$12.25	$12.30
Purchase #5	$112.45	13.830%	$128.0018	$128.00	$128.00	$128.00
Purchase #6	$95.94	5.676%	$101.3856	$101.39	$101.40	$101.40
Purchase #7	$140.50	6.352%	$149.4246	$149.42	$149.40	$149.40
7 purchase totals =	$812.59		$891.8971	$891.89	$891.90	$891.90