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	$149.49	4.488%	$156.1991	$156.20	$156.20	$156.20
Purchase #2	$132.99	12.455%	$149.5539	$149.55	$149.55	$149.60
Purchase #3	$61.58	12.271%	$69.1365	$69.14	$69.15	$69.10
Purchase #4	$19.39	7.827%	$20.9077	$20.91	$20.90	$20.90
Purchase #5	$89.51	12.594%	$100.7829	$100.78	$100.80	$100.80
Purchase #6	$89.86	11.325%	$100.0366	$100.04	$100.05	$100.00
Purchase #7	$75.58	6.362%	$80.3884	$80.39	$80.40	$80.40
7 purchase totals =	$618.40		$677.0051	$677.01	$677.05	$677.00