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	$31.39	8.808%	$34.1548	$34.15	$34.15	$34.20
Purchase #2	$29.57	4.502%	$30.9012	$30.90	$30.90	$30.90
Purchase #3	$229.98	7.744%	$247.7897	$247.79	$247.80	$247.80
Purchase #4	$239.57	6.707%	$255.638	$255.64	$255.65	$255.60
Purchase #5	$200.71	6.686%	$214.1295	$214.13	$214.15	$214.10
Purchase #6	$69.26	3.823%	$71.9078	$71.91	$71.90	$71.90
Purchase #7	$112.94	9.385%	$123.5394	$123.54	$123.55	$123.50
7 purchase totals =	$913.42		$978.0604	$978.06	$978.10	$978.00