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	$8.59	3.841%	$8.9199	$8.92	$8.90	$8.90
Purchase #2	$233.90	9.299%	$255.6504	$255.65	$255.65	$255.70
Purchase #3	$132.91	4.157%	$138.4351	$138.44	$138.45	$138.40
Purchase #4	$39.56	13.762%	$45.0042	$45.00	$45.00	$45.00
Purchase #5	$34.26	10.433%	$37.8343	$37.83	$37.85	$37.80
Purchase #6	$242.41	3.244%	$250.2738	$250.27	$250.25	$250.30
Purchase #7	$78.43	13.120%	$88.72	$88.72	$88.70	$88.70
7 purchase totals =	$770.06		$824.8377	$824.83	$824.80	$824.80