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	$35.89	5.564%	$37.8869	$37.89	$37.90	$37.90
Purchase #2	$157.75	11.463%	$175.8329	$175.83	$175.85	$175.80
Purchase #3	$138.27	3.332%	$142.8772	$142.88	$142.90	$142.90
Purchase #4	$11.30	8.453%	$12.2552	$12.26	$12.25	$12.30
Purchase #5	$180.86	13.525%	$205.3213	$205.32	$205.30	$205.30
Purchase #6	$135.34	11.247%	$150.5617	$150.56	$150.55	$150.60
Purchase #7	$224.65	10.171%	$247.4992	$247.50	$247.50	$247.50
7 purchase totals =	$884.06		$972.2344	$972.24	$972.25	$972.30