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	$141.93	3.869%	$147.4213	$147.42	$147.40	$147.40
Purchase #2	$223.73	13.467%	$253.8597	$253.86	$253.85	$253.90
Purchase #3	$68.78	3.854%	$71.4308	$71.43	$71.45	$71.40
Purchase #4	$88.78	4.175%	$92.4866	$92.49	$92.50	$92.50
Purchase #5	$123.99	10.706%	$137.2644	$137.26	$137.25	$137.30
Purchase #6	$99.49	3.625%	$103.0965	$103.10	$103.10	$103.10
Purchase #7	$99.82	6.252%	$106.0607	$106.06	$106.05	$106.10
7 purchase totals =	$846.52		$911.6200	$911.62	$911.60	$911.70