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	$90.62	11.363%	$100.9172	$100.92	$100.90	$100.90
Purchase #2	$29.26	5.503%	$30.8702	$30.87	$30.85	$30.90
Purchase #3	$191.81	9.131%	$209.3242	$209.32	$209.30	$209.30
Purchase #4	$238.26	3.271%	$246.0535	$246.05	$246.05	$246.10
Purchase #5	$230.51	4.505%	$240.8945	$240.89	$240.90	$240.90
Purchase #6	$51.38	4.163%	$53.5189	$53.52	$53.50	$53.50
Purchase #7	$101.52	9.562%	$111.2273	$111.23	$111.25	$111.20
7 purchase totals =	$933.36		$992.8058	$992.80	$992.75	$992.80