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	$239.43	7.684%	$257.8278	$257.83	$257.85	$257.80
Purchase #2	$192.50	3.720%	$199.661	$199.66	$199.65	$199.70
Purchase #3	$81.46	9.834%	$89.4708	$89.47	$89.45	$89.50
Purchase #4	$34.81	6.485%	$37.0674	$37.07	$37.05	$37.10
Purchase #5	$72.26	6.616%	$77.0407	$77.04	$77.05	$77.00
Purchase #6	$22.38	3.290%	$23.1163	$23.12	$23.10	$23.10
Purchase #7	$93.80	5.690%	$99.1372	$99.14	$99.15	$99.10
7 purchase totals =	$736.64		$783.3212	$783.33	$783.30	$783.30