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	$109.83	12.660%	$123.7345	$123.73	$123.75	$123.70
Purchase #2	$88.86	3.453%	$91.9283	$91.93	$91.95	$91.90
Purchase #3	$219.26	11.510%	$244.4968	$244.50	$244.50	$244.50
Purchase #4	$43.40	4.486%	$45.3469	$45.35	$45.35	$45.30
Purchase #5	$228.89	9.723%	$251.145	$251.15	$251.15	$251.10
Purchase #6	$237.51	6.773%	$253.5966	$253.60	$253.60	$253.60
Purchase #7	$19.47	6.182%	$20.6736	$20.67	$20.65	$20.70
7 purchase totals =	$947.22		$1,030.9217	$1,030.93	$1,030.95	$1,030.80