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	$16.83	7.329%	$18.0635	$18.06	$18.05	$18.10
Purchase #2	$230.26	3.542%	$238.4158	$238.42	$238.40	$238.40
Purchase #3	$56.91	8.651%	$61.8333	$61.83	$61.85	$61.80
Purchase #4	$244.28	9.378%	$267.1886	$267.19	$267.20	$267.20
Purchase #5	$211.54	9.549%	$231.74	$231.74	$231.75	$231.70
Purchase #6	$184.33	3.594%	$190.9548	$190.95	$190.95	$191.00
Purchase #7	$74.50	5.657%	$78.7145	$78.71	$78.70	$78.70
7 purchase totals =	$1,018.65		$1,086.9105	$1,086.90	$1,086.90	$1,086.90