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	$161.43	4.174%	$168.1681	$168.17	$168.15	$168.20
Purchase #2	$30.53	7.788%	$32.9077	$32.91	$32.90	$32.90
Purchase #3	$231.36	12.114%	$259.387	$259.39	$259.40	$259.40
Purchase #4	$33.68	5.495%	$35.5307	$35.53	$35.55	$35.50
Purchase #5	$8.28	7.539%	$8.9042	$8.90	$8.90	$8.90
Purchase #6	$230.72	5.456%	$243.3081	$243.31	$243.30	$243.30
Purchase #7	$151.70	13.847%	$172.7059	$172.71	$172.70	$172.70
7 purchase totals =	$847.70		$920.9117	$920.92	$920.90	$920.90