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	$112.96	3.386%	$116.7848	$116.78	$116.80	$116.80
Purchase #2	$128.42	13.768%	$146.1009	$146.10	$146.10	$146.10
Purchase #3	$54.81	8.713%	$59.5856	$59.59	$59.60	$59.60
Purchase #4	$141.91	10.443%	$156.7297	$156.73	$156.75	$156.70
Purchase #5	$244.52	6.168%	$259.602	$259.60	$259.60	$259.60
Purchase #6	$160.28	4.310%	$167.1881	$167.19	$167.20	$167.20
Purchase #7	$88.45	4.721%	$92.6257	$92.63	$92.65	$92.60
7 purchase totals =	$931.35		$998.6168	$998.62	$998.70	$998.60