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	$123.26	3.423%	$127.4792	$127.48	$127.50	$127.50
Purchase #2	$192.94	3.723%	$200.1232	$200.12	$200.10	$200.10
Purchase #3	$102.45	6.283%	$108.8869	$108.89	$108.90	$108.90
Purchase #4	$244.57	5.852%	$258.8822	$258.88	$258.90	$258.90
Purchase #5	$227.93	10.856%	$252.6741	$252.67	$252.65	$252.70
Purchase #6	$34.63	8.394%	$37.5368	$37.54	$37.55	$37.50
Purchase #7	$23.50	13.680%	$26.7148	$26.71	$26.70	$26.70
7 purchase totals =	$949.28		$1,012.2972	$1,012.29	$1,012.30	$1,012.30