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	$95.61	4.163%	$99.5902	$99.59	$99.60	$99.60
Purchase #2	$20.26	11.653%	$22.6209	$22.62	$22.60	$22.60
Purchase #3	$128.58	6.765%	$137.2784	$137.28	$137.30	$137.30
Purchase #4	$114.77	3.676%	$118.9889	$118.99	$119.00	$119.00
Purchase #5	$117.57	8.535%	$127.6046	$127.60	$127.60	$127.60
Purchase #6	$134.65	12.395%	$151.3399	$151.34	$151.35	$151.30
Purchase #7	$158.25	8.692%	$172.0051	$172.01	$172.00	$172.00
7 purchase totals =	$769.69		$829.4280	$829.43	$829.45	$829.40