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	$136.28	7.425%	$146.3988	$146.40	$146.40	$146.40
Purchase #2	$127.42	4.182%	$132.7487	$132.75	$132.75	$132.70
Purchase #3	$204.95	7.600%	$220.5262	$220.53	$220.55	$220.50
Purchase #4	$104.62	6.370%	$111.2843	$111.28	$111.30	$111.30
Purchase #5	$35.54	13.420%	$40.3095	$40.31	$40.30	$40.30
Purchase #6	$79.94	7.150%	$85.6557	$85.66	$85.65	$85.70
Purchase #7	$78.87	12.770%	$88.9417	$88.94	$88.95	$88.90
7 purchase totals =	$767.62		$825.8649	$825.87	$825.90	$825.80