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	$244.30	4.128%	$254.3847	$254.38	$254.40	$254.40
Purchase #2	$131.47	10.253%	$144.9496	$144.95	$144.95	$144.90
Purchase #3	$112.44	8.301%	$121.7736	$121.77	$121.75	$121.80
Purchase #4	$192.89	12.852%	$217.6802	$217.68	$217.70	$217.70
Purchase #5	$118.89	8.312%	$128.7721	$128.77	$128.75	$128.80
Purchase #6	$100.31	5.461%	$105.7879	$105.79	$105.80	$105.80
Purchase #7	$135.88	10.562%	$150.2316	$150.23	$150.25	$150.20
7 purchase totals =	$1,036.18		$1,123.5797	$1,123.57	$1,123.60	$1,123.60