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	$233.73	9.319%	$255.5113	$255.51	$255.50	$255.50
Purchase #2	$18.93	10.238%	$20.8681	$20.87	$20.85	$20.90
Purchase #3	$90.99	11.852%	$101.7741	$101.77	$101.75	$101.80
Purchase #4	$165.52	9.528%	$181.2907	$181.29	$181.30	$181.30
Purchase #5	$114.95	10.413%	$126.9197	$126.92	$126.90	$126.90
Purchase #6	$222.51	6.636%	$237.2758	$237.28	$237.30	$237.30
Purchase #7	$24.31	13.731%	$27.648	$27.65	$27.65	$27.60
7 purchase totals =	$870.94		$951.2877	$951.29	$951.25	$951.30