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	$18.75	7.296%	$20.118	$20.12	$20.10	$20.10
Purchase #2	$63.82	10.133%	$70.2869	$70.29	$70.30	$70.30
Purchase #3	$30.51	10.207%	$33.6242	$33.62	$33.60	$33.60
Purchase #4	$172.66	13.254%	$195.5444	$195.54	$195.55	$195.50
Purchase #5	$108.64	9.553%	$119.0184	$119.02	$119.00	$119.00
Purchase #6	$60.59	3.607%	$62.7755	$62.78	$62.80	$62.80
Purchase #7	$123.62	13.609%	$140.4434	$140.44	$140.45	$140.40
7 purchase totals =	$578.59		$641.8108	$641.81	$641.80	$641.70