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	$36.31	5.117%	$38.168	$38.17	$38.15	$38.20
Purchase #2	$242.98	9.801%	$266.7945	$266.79	$266.80	$266.80
Purchase #3	$18.83	4.707%	$19.7163	$19.72	$19.70	$19.70
Purchase #4	$9.91	13.610%	$11.2588	$11.26	$11.25	$11.30
Purchase #5	$166.48	10.247%	$183.5392	$183.54	$183.55	$183.50
Purchase #6	$34.61	9.556%	$37.9173	$37.92	$37.90	$37.90
Purchase #7	$158.33	8.181%	$171.283	$171.28	$171.30	$171.30
7 purchase totals =	$667.45		$728.6771	$728.68	$728.65	$728.70