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	$14.76	6.209%	$15.6764	$15.68	$15.70	$15.70
Purchase #2	$211.55	8.301%	$229.1108	$229.11	$229.10	$229.10
Purchase #3	$127.84	10.350%	$141.0714	$141.07	$141.05	$141.10
Purchase #4	$55.82	6.610%	$59.5097	$59.51	$59.50	$59.50
Purchase #5	$222.49	13.152%	$251.7519	$251.75	$251.75	$251.80
Purchase #6	$77.38	7.697%	$83.3359	$83.34	$83.35	$83.30
Purchase #7	$158.42	8.109%	$171.2663	$171.27	$171.25	$171.30
7 purchase totals =	$868.26		$951.7224	$951.73	$951.70	$951.80