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	$129.94	11.211%	$144.5076	$144.51	$144.50	$144.50
Purchase #2	$102.39	4.150%	$106.6392	$106.64	$106.65	$106.60
Purchase #3	$52.65	12.390%	$59.1733	$59.17	$59.15	$59.20
Purchase #4	$56.81	5.541%	$59.9578	$59.96	$59.95	$60.00
Purchase #5	$20.73	6.707%	$22.1204	$22.12	$22.10	$22.10
Purchase #6	$161.85	5.294%	$170.4183	$170.42	$170.40	$170.40
Purchase #7	$26.51	3.668%	$27.4824	$27.48	$27.50	$27.50
7 purchase totals =	$550.88		$590.2990	$590.30	$590.25	$590.30