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	$110.86	11.478%	$123.5845	$123.58	$123.60	$123.60
Purchase #2	$215.56	12.264%	$241.9963	$242.00	$242.00	$242.00
Purchase #3	$115.78	6.370%	$123.1552	$123.16	$123.15	$123.20
Purchase #4	$234.35	12.785%	$264.3116	$264.31	$264.30	$264.30
Purchase #5	$49.42	7.332%	$53.0435	$53.04	$53.05	$53.00
Purchase #6	$127.50	13.594%	$144.8324	$144.83	$144.85	$144.80
Purchase #7	$192.36	8.222%	$208.1758	$208.18	$208.20	$208.20
7 purchase totals =	$1,045.83		$1,159.0993	$1,159.10	$1,159.15	$1,159.10