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	$20.65	7.209%	$22.1387	$22.14	$22.15	$22.10
Purchase #2	$171.92	10.663%	$190.2518	$190.25	$190.25	$190.30
Purchase #3	$160.37	7.427%	$172.2807	$172.28	$172.30	$172.30
Purchase #4	$122.33	11.222%	$136.0579	$136.06	$136.05	$136.10
Purchase #5	$109.74	12.749%	$123.7308	$123.73	$123.75	$123.70
Purchase #6	$9.49	6.727%	$10.1284	$10.13	$10.15	$10.10
Purchase #7	$170.48	8.585%	$185.1157	$185.12	$185.10	$185.10
7 purchase totals =	$764.98		$839.7040	$839.71	$839.75	$839.70