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	$90.49	11.263%	$100.6819	$100.68	$100.70	$100.70
Purchase #2	$89.64	9.810%	$98.4337	$98.43	$98.45	$98.40
Purchase #3	$100.29	4.784%	$105.0879	$105.09	$105.10	$105.10
Purchase #4	$172.78	3.187%	$178.2865	$178.29	$178.30	$178.30
Purchase #5	$103.42	9.734%	$113.4869	$113.49	$113.50	$113.50
Purchase #6	$81.59	9.316%	$89.1909	$89.19	$89.20	$89.20
Purchase #7	$35.60	4.181%	$37.0884	$37.09	$37.10	$37.10
7 purchase totals =	$673.81		$722.2562	$722.26	$722.35	$722.30