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	$131.54	5.222%	$138.409	$138.41	$138.40	$138.40
Purchase #2	$165.48	4.857%	$173.5174	$173.52	$173.50	$173.50
Purchase #3	$86.84	11.301%	$96.6538	$96.65	$96.65	$96.70
Purchase #4	$158.47	9.730%	$173.8891	$173.89	$173.90	$173.90
Purchase #5	$39.96	7.252%	$42.8579	$42.86	$42.85	$42.90
Purchase #6	$91.26	3.508%	$94.4614	$94.46	$94.45	$94.50
Purchase #7	$75.26	13.125%	$85.1379	$85.14	$85.15	$85.10
7 purchase totals =	$748.81		$804.9265	$804.93	$804.90	$805.00