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	$9.45	12.866%	$10.6658	$10.67	$10.65	$10.70
Purchase #2	$143.81	6.675%	$153.4093	$153.41	$153.40	$153.40
Purchase #3	$20.92	4.749%	$21.9135	$21.91	$21.90	$21.90
Purchase #4	$44.77	11.812%	$50.0582	$50.06	$50.05	$50.10
Purchase #5	$27.26	10.519%	$30.1275	$30.13	$30.15	$30.10
Purchase #6	$176.95	11.118%	$196.6233	$196.62	$196.60	$196.60
Purchase #7	$33.26	6.750%	$35.5051	$35.51	$35.50	$35.50
7 purchase totals =	$456.42		$498.3027	$498.31	$498.25	$498.30