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	$18.77	7.460%	$20.1702	$20.17	$20.15	$20.20
Purchase #2	$159.25	8.272%	$172.4232	$172.42	$172.40	$172.40
Purchase #3	$53.50	6.370%	$56.908	$56.91	$56.90	$56.90
Purchase #4	$182.78	10.793%	$202.5074	$202.51	$202.50	$202.50
Purchase #5	$113.57	12.403%	$127.6561	$127.66	$127.65	$127.70
Purchase #6	$23.88	6.345%	$25.3952	$25.40	$25.40	$25.40
Purchase #7	$90.57	11.703%	$101.1694	$101.17	$101.15	$101.20
7 purchase totals =	$642.32		$706.2295	$706.24	$706.15	$706.30