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	$37.69	8.450%	$40.8748	$40.87	$40.85	$40.90
Purchase #2	$79.81	8.289%	$86.4255	$86.43	$86.45	$86.40
Purchase #3	$147.83	3.608%	$153.1637	$153.16	$153.15	$153.20
Purchase #4	$107.52	3.686%	$111.4832	$111.48	$111.50	$111.50
Purchase #5	$137.28	8.227%	$148.574	$148.57	$148.55	$148.60
Purchase #6	$73.45	7.632%	$79.0557	$79.06	$79.05	$79.10
Purchase #7	$35.44	8.557%	$38.4726	$38.47	$38.45	$38.50
7 purchase totals =	$619.02		$658.0495	$658.04	$658.00	$658.20