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	$70.25	11.237%	$78.144	$78.14	$78.15	$78.10
Purchase #2	$154.57	10.253%	$170.4181	$170.42	$170.40	$170.40
Purchase #3	$148.49	7.583%	$159.75	$159.75	$159.75	$159.80
Purchase #4	$64.52	3.147%	$66.5504	$66.55	$66.55	$66.60
Purchase #5	$137.56	7.277%	$147.5702	$147.57	$147.55	$147.60
Purchase #6	$92.72	8.744%	$100.8274	$100.83	$100.85	$100.80
Purchase #7	$51.65	13.225%	$58.4807	$58.48	$58.50	$58.50
7 purchase totals =	$719.76		$781.7408	$781.74	$781.75	$781.80