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	$126.68	11.363%	$141.0746	$141.07	$141.05	$141.10
Purchase #2	$225.36	13.280%	$255.2878	$255.29	$255.30	$255.30
Purchase #3	$160.33	8.437%	$173.857	$173.86	$173.85	$173.90
Purchase #4	$83.52	6.655%	$89.0783	$89.08	$89.10	$89.10
Purchase #5	$81.41	12.327%	$91.4454	$91.45	$91.45	$91.40
Purchase #6	$49.69	9.617%	$54.4687	$54.47	$54.45	$54.50
Purchase #7	$22.77	8.672%	$24.7446	$24.74	$24.75	$24.70
7 purchase totals =	$749.76		$829.9564	$829.96	$829.95	$830.00