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	$30.89	4.600%	$32.3109	$32.31	$32.30	$32.30
Purchase #2	$63.76	7.485%	$68.5324	$68.53	$68.55	$68.50
Purchase #3	$34.90	7.222%	$37.4205	$37.42	$37.40	$37.40
Purchase #4	$76.88	4.242%	$80.1412	$80.14	$80.15	$80.10
Purchase #5	$139.43	9.563%	$152.7637	$152.76	$152.75	$152.80
Purchase #6	$82.66	10.343%	$91.2095	$91.21	$91.20	$91.20
Purchase #7	$27.91	5.748%	$29.5143	$29.51	$29.50	$29.50
7 purchase totals =	$456.43		$491.8925	$491.88	$491.85	$491.80