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	$21.82	9.502%	$23.8933	$23.89	$23.90	$23.90
Purchase #2	$146.25	10.806%	$162.0538	$162.05	$162.05	$162.10
Purchase #3	$11.76	6.760%	$12.555	$12.56	$12.55	$12.60
Purchase #4	$28.83	13.143%	$32.6191	$32.62	$32.60	$32.60
Purchase #5	$71.56	8.571%	$77.6934	$77.69	$77.70	$77.70
Purchase #6	$35.80	4.429%	$37.3856	$37.39	$37.40	$37.40
Purchase #7	$88.51	6.108%	$93.9162	$93.92	$93.90	$93.90
7 purchase totals =	$404.53		$440.1164	$440.12	$440.10	$440.20