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	$217.83	13.498%	$247.2327	$247.23	$247.25	$247.20
Purchase #2	$242.66	6.658%	$258.8163	$258.82	$258.80	$258.80
Purchase #3	$177.65	10.446%	$196.2073	$196.21	$196.20	$196.20
Purchase #4	$50.96	13.502%	$57.8406	$57.84	$57.85	$57.80
Purchase #5	$121.32	4.805%	$127.1494	$127.15	$127.15	$127.10
Purchase #6	$217.54	12.487%	$244.7042	$244.70	$244.70	$244.70
Purchase #7	$70.83	8.451%	$76.8158	$76.82	$76.80	$76.80
7 purchase totals =	$1,098.79		$1,208.7663	$1,208.77	$1,208.75	$1,208.60