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	$169.39	12.574%	$190.6891	$190.69	$190.70	$190.70
Purchase #2	$156.65	3.428%	$162.02	$162.02	$162.00	$162.00
Purchase #3	$78.92	4.551%	$82.5116	$82.51	$82.50	$82.50
Purchase #4	$222.84	3.268%	$230.1224	$230.12	$230.10	$230.10
Purchase #5	$55.59	3.399%	$57.4795	$57.48	$57.50	$57.50
Purchase #6	$58.52	13.223%	$66.2581	$66.26	$66.25	$66.30
Purchase #7	$54.54	11.436%	$60.7772	$60.78	$60.80	$60.80
7 purchase totals =	$796.45		$849.8579	$849.86	$849.85	$849.90