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	$29.72	8.684%	$32.3009	$32.30	$32.30	$32.30
Purchase #2	$49.52	11.234%	$55.0831	$55.08	$55.10	$55.10
Purchase #3	$29.55	7.257%	$31.6944	$31.69	$31.70	$31.70
Purchase #4	$173.59	9.778%	$190.5636	$190.56	$190.55	$190.60
Purchase #5	$94.80	4.563%	$99.1257	$99.13	$99.15	$99.10
Purchase #6	$37.74	13.375%	$42.7877	$42.79	$42.80	$42.80
Purchase #7	$112.59	13.369%	$127.6422	$127.64	$127.65	$127.60
7 purchase totals =	$527.51		$579.1976	$579.19	$579.25	$579.20