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	$128.67	13.870%	$146.5165	$146.52	$146.50	$146.50
Purchase #2	$49.46	11.595%	$55.1949	$55.19	$55.20	$55.20
Purchase #3	$20.89	8.748%	$22.7175	$22.72	$22.70	$22.70
Purchase #4	$136.83	7.181%	$146.6558	$146.66	$146.65	$146.70
Purchase #5	$54.73	7.610%	$58.895	$58.90	$58.90	$58.90
Purchase #6	$77.52	9.826%	$85.1371	$85.14	$85.15	$85.10
Purchase #7	$45.74	5.680%	$48.338	$48.34	$48.35	$48.30
7 purchase totals =	$513.84		$563.4548	$563.47	$563.45	$563.40