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	$153.60	4.488%	$160.4936	$160.49	$160.50	$160.50
Purchase #2	$32.77	5.260%	$34.4937	$34.49	$34.50	$34.50
Purchase #3	$11.61	6.845%	$12.4047	$12.40	$12.40	$12.40
Purchase #4	$171.27	12.413%	$192.5297	$192.53	$192.55	$192.50
Purchase #5	$103.31	5.646%	$109.1429	$109.14	$109.15	$109.10
Purchase #6	$243.69	5.297%	$256.5983	$256.60	$256.60	$256.60
Purchase #7	$39.73	13.547%	$45.1122	$45.11	$45.10	$45.10
7 purchase totals =	$755.98		$810.7751	$810.76	$810.80	$810.70