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	$214.91	11.356%	$239.3152	$239.32	$239.30	$239.30
Purchase #2	$47.94	11.670%	$53.5346	$53.53	$53.55	$53.50
Purchase #3	$205.60	6.667%	$219.3074	$219.31	$219.30	$219.30
Purchase #4	$40.36	13.519%	$45.8163	$45.82	$45.80	$45.80
Purchase #5	$71.77	3.319%	$74.152	$74.15	$74.15	$74.20
Purchase #6	$165.37	10.210%	$182.2543	$182.25	$182.25	$182.30
Purchase #7	$242.82	5.351%	$255.8133	$255.81	$255.80	$255.80
7 purchase totals =	$988.77		$1,070.1931	$1,070.19	$1,070.15	$1,070.20