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	$42.92	11.446%	$47.8326	$47.83	$47.85	$47.80
Purchase #2	$66.64	6.326%	$70.8556	$70.86	$70.85	$70.90
Purchase #3	$201.54	10.541%	$222.7843	$222.78	$222.80	$222.80
Purchase #4	$223.37	4.502%	$233.4261	$233.43	$233.45	$233.40
Purchase #5	$15.74	13.853%	$17.9205	$17.92	$17.90	$17.90
Purchase #6	$108.31	3.164%	$111.7369	$111.74	$111.75	$111.70
Purchase #7	$114.58	9.301%	$125.2371	$125.24	$125.25	$125.20
7 purchase totals =	$773.10		$829.7931	$829.80	$829.85	$829.70