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	$172.94	4.412%	$180.5701	$180.57	$180.55	$180.60
Purchase #2	$238.68	6.601%	$254.4353	$254.44	$254.45	$254.40
Purchase #3	$47.42	11.225%	$52.7429	$52.74	$52.75	$52.70
Purchase #4	$135.46	3.778%	$140.5777	$140.58	$140.60	$140.60
Purchase #5	$6.90	5.648%	$7.2897	$7.29	$7.30	$7.30
Purchase #6	$211.29	12.284%	$237.2449	$237.24	$237.25	$237.20
Purchase #7	$130.41	12.346%	$146.5104	$146.51	$146.50	$146.50
7 purchase totals =	$943.10		$1,019.3710	$1,019.37	$1,019.40	$1,019.30