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	$41.89	11.687%	$46.7857	$46.79	$46.80	$46.80
Purchase #2	$73.58	12.157%	$82.5251	$82.53	$82.55	$82.50
Purchase #3	$67.82	3.733%	$70.3517	$70.35	$70.35	$70.40
Purchase #4	$80.32	11.413%	$89.4869	$89.49	$89.50	$89.50
Purchase #5	$58.25	6.605%	$62.0974	$62.10	$62.10	$62.10
Purchase #6	$132.82	9.575%	$145.5375	$145.54	$145.55	$145.50
Purchase #7	$157.41	7.852%	$169.7698	$169.77	$169.75	$169.80
7 purchase totals =	$612.09		$666.5541	$666.57	$666.60	$666.60