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	$23.26	13.707%	$26.4482	$26.45	$26.45	$26.40
Purchase #2	$78.84	13.506%	$89.4881	$89.49	$89.50	$89.50
Purchase #3	$248.55	10.768%	$275.3139	$275.31	$275.30	$275.30
Purchase #4	$118.99	11.700%	$132.9118	$132.91	$132.90	$132.90
Purchase #5	$86.28	3.550%	$89.3429	$89.34	$89.35	$89.30
Purchase #6	$165.87	5.636%	$175.2184	$175.22	$175.20	$175.20
Purchase #7	$128.61	13.504%	$145.9775	$145.98	$146.00	$146.00
7 purchase totals =	$850.40		$934.7008	$934.70	$934.70	$934.60