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	$35.74	10.191%	$39.3823	$39.38	$39.40	$39.40
Purchase #2	$131.65	12.577%	$148.2076	$148.21	$148.20	$148.20
Purchase #3	$39.62	10.504%	$43.7817	$43.78	$43.80	$43.80
Purchase #4	$132.27	3.461%	$136.8479	$136.85	$136.85	$136.80
Purchase #5	$65.52	7.582%	$70.4877	$70.49	$70.50	$70.50
Purchase #6	$51.48	7.834%	$55.5129	$55.51	$55.50	$55.50
Purchase #7	$157.60	11.408%	$175.579	$175.58	$175.60	$175.60
7 purchase totals =	$613.88		$669.7991	$669.80	$669.85	$669.80