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	$176.35	7.409%	$189.4158	$189.42	$189.40	$189.40
Purchase #2	$190.83	5.273%	$200.8925	$200.89	$200.90	$200.90
Purchase #3	$57.72	13.444%	$65.4799	$65.48	$65.50	$65.50
Purchase #4	$96.29	9.156%	$105.1063	$105.11	$105.10	$105.10
Purchase #5	$30.80	11.537%	$34.3534	$34.35	$34.35	$34.40
Purchase #6	$155.72	11.175%	$173.1217	$173.12	$173.10	$173.10
Purchase #7	$73.76	6.844%	$78.8081	$78.81	$78.80	$78.80
7 purchase totals =	$781.47		$847.1777	$847.18	$847.15	$847.20