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	$153.83	3.867%	$159.7786	$159.78	$159.80	$159.80
Purchase #2	$239.67	6.751%	$255.8501	$255.85	$255.85	$255.90
Purchase #3	$249.30	5.425%	$262.8245	$262.82	$262.80	$262.80
Purchase #4	$232.36	9.650%	$254.7827	$254.78	$254.80	$254.80
Purchase #5	$111.85	4.262%	$116.617	$116.62	$116.60	$116.60
Purchase #6	$216.68	8.813%	$235.776	$235.78	$235.80	$235.80
Purchase #7	$43.31	4.261%	$45.1554	$45.16	$45.15	$45.20
7 purchase totals =	$1,247.00		$1,330.7843	$1,330.79	$1,330.80	$1,330.90