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	$33.29	12.701%	$37.5182	$37.52	$37.50	$37.50
Purchase #2	$173.29	13.307%	$196.3497	$196.35	$196.35	$196.30
Purchase #3	$143.27	12.850%	$161.6802	$161.68	$161.70	$161.70
Purchase #4	$164.32	10.363%	$181.3485	$181.35	$181.35	$181.30
Purchase #5	$91.45	4.836%	$95.8725	$95.87	$95.85	$95.90
Purchase #6	$28.89	3.294%	$29.8416	$29.84	$29.85	$29.80
Purchase #7	$250.48	3.866%	$260.1636	$260.16	$260.15	$260.20
7 purchase totals =	$884.99		$962.7743	$962.77	$962.75	$962.70