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	$184.26	13.372%	$208.8992	$208.90	$208.90	$208.90
Purchase #2	$240.52	4.168%	$250.5449	$250.54	$250.55	$250.50
Purchase #3	$105.91	13.334%	$120.032	$120.03	$120.05	$120.00
Purchase #4	$222.41	7.314%	$238.6771	$238.68	$238.70	$238.70
Purchase #5	$231.77	6.769%	$247.4585	$247.46	$247.45	$247.50
Purchase #6	$214.89	10.254%	$236.9248	$236.92	$236.90	$236.90
Purchase #7	$17.25	10.573%	$19.0738	$19.07	$19.05	$19.10
7 purchase totals =	$1,217.01		$1,321.6103	$1,321.60	$1,321.60	$1,321.60