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	$84.57	4.382%	$88.2759	$88.28	$88.30	$88.30
Purchase #2	$146.38	3.523%	$151.537	$151.54	$151.55	$151.50
Purchase #3	$74.94	12.656%	$84.4244	$84.42	$84.40	$84.40
Purchase #4	$168.85	9.802%	$185.4007	$185.40	$185.40	$185.40
Purchase #5	$167.42	4.586%	$175.0979	$175.10	$175.10	$175.10
Purchase #6	$134.50	7.525%	$144.6211	$144.62	$144.60	$144.60
Purchase #7	$9.83	3.594%	$10.1833	$10.18	$10.20	$10.20
7 purchase totals =	$786.49		$839.5403	$839.54	$839.55	$839.50