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	$10.45	11.258%	$11.6265	$11.63	$11.65	$11.60
Purchase #2	$240.45	5.738%	$254.247	$254.25	$254.25	$254.20
Purchase #3	$125.91	8.701%	$136.8654	$136.87	$136.85	$136.90
Purchase #4	$29.72	9.439%	$32.5253	$32.53	$32.55	$32.50
Purchase #5	$48.76	4.410%	$50.9103	$50.91	$50.90	$50.90
Purchase #6	$117.79	8.178%	$127.4229	$127.42	$127.40	$127.40
Purchase #7	$170.48	11.463%	$190.0221	$190.02	$190.00	$190.00
7 purchase totals =	$743.56		$803.6195	$803.63	$803.60	$803.50