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	$38.32	11.438%	$42.703	$42.70	$42.70	$42.70
Purchase #2	$136.48	6.282%	$145.0537	$145.05	$145.05	$145.10
Purchase #3	$153.65	13.533%	$174.4435	$174.44	$174.45	$174.40
Purchase #4	$158.77	3.378%	$164.1333	$164.13	$164.15	$164.10
Purchase #5	$153.40	12.532%	$172.6241	$172.62	$172.60	$172.60
Purchase #6	$224.80	13.198%	$254.4691	$254.47	$254.45	$254.50
Purchase #7	$86.46	13.845%	$98.4304	$98.43	$98.45	$98.40
7 purchase totals =	$951.88		$1,051.8571	$1,051.84	$1,051.85	$1,051.80