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	$93.83	5.464%	$98.9569	$98.96	$98.95	$99.00
Purchase #2	$223.69	10.793%	$247.8329	$247.83	$247.85	$247.80
Purchase #3	$224.45	6.142%	$238.2357	$238.24	$238.25	$238.20
Purchase #4	$66.28	6.294%	$70.4517	$70.45	$70.45	$70.50
Purchase #5	$66.46	10.301%	$73.306	$73.31	$73.30	$73.30
Purchase #6	$151.96	13.616%	$172.6509	$172.65	$172.65	$172.70
Purchase #7	$91.37	7.544%	$98.263	$98.26	$98.25	$98.30
7 purchase totals =	$918.04		$999.6971	$999.70	$999.70	$999.80