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	$92.50	11.690%	$103.3133	$103.31	$103.30	$103.30
Purchase #2	$158.49	8.562%	$172.0599	$172.06	$172.05	$172.10
Purchase #3	$47.98	5.818%	$50.7715	$50.77	$50.75	$50.80
Purchase #4	$59.89	10.453%	$66.1503	$66.15	$66.15	$66.20
Purchase #5	$165.63	8.378%	$179.5065	$179.51	$179.50	$179.50
Purchase #6	$23.65	7.587%	$25.4443	$25.44	$25.45	$25.40
Purchase #7	$214.84	10.832%	$238.1115	$238.11	$238.10	$238.10
7 purchase totals =	$762.98		$835.3573	$835.35	$835.30	$835.40