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	$49.58	11.684%	$55.3729	$55.37	$55.35	$55.40
Purchase #2	$141.94	12.290%	$159.3844	$159.38	$159.40	$159.40
Purchase #3	$101.87	7.296%	$109.3024	$109.30	$109.30	$109.30
Purchase #4	$48.32	4.551%	$50.519	$50.52	$50.50	$50.50
Purchase #5	$92.40	7.864%	$99.6663	$99.67	$99.65	$99.70
Purchase #6	$217.65	10.471%	$240.4401	$240.44	$240.45	$240.40
Purchase #7	$170.55	4.503%	$178.2299	$178.23	$178.25	$178.20
7 purchase totals =	$822.31		$892.9150	$892.91	$892.90	$892.90