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	$46.46	12.571%	$52.3005	$52.30	$52.30	$52.30
Purchase #2	$29.99	7.445%	$32.2228	$32.22	$32.20	$32.20
Purchase #3	$231.50	8.477%	$251.1243	$251.12	$251.10	$251.10
Purchase #4	$36.73	10.388%	$40.5455	$40.55	$40.55	$40.50
Purchase #5	$82.82	8.448%	$89.8166	$89.82	$89.80	$89.80
Purchase #6	$152.34	5.414%	$160.5877	$160.59	$160.60	$160.60
Purchase #7	$98.97	13.209%	$112.0429	$112.04	$112.05	$112.00
7 purchase totals =	$678.81		$738.6403	$738.64	$738.60	$738.50