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	$158.54	7.392%	$170.2593	$170.26	$170.25	$170.30
Purchase #2	$77.78	6.353%	$82.7214	$82.72	$82.70	$82.70
Purchase #3	$246.82	3.647%	$255.8215	$255.82	$255.80	$255.80
Purchase #4	$65.63	12.146%	$73.6014	$73.60	$73.60	$73.60
Purchase #5	$110.50	4.665%	$115.6548	$115.65	$115.65	$115.70
Purchase #6	$197.76	10.745%	$219.0093	$219.01	$219.00	$219.00
Purchase #7	$50.69	6.727%	$54.0999	$54.10	$54.10	$54.10
7 purchase totals =	$907.72		$971.1676	$971.16	$971.10	$971.20