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	$98.92	12.513%	$111.2979	$111.30	$111.30	$111.30
Purchase #2	$212.63	12.690%	$239.6127	$239.61	$239.60	$239.60
Purchase #3	$104.93	6.196%	$111.4315	$111.43	$111.45	$111.40
Purchase #4	$101.67	4.677%	$106.4251	$106.43	$106.45	$106.40
Purchase #5	$144.31	10.246%	$159.096	$159.10	$159.10	$159.10
Purchase #6	$52.37	4.356%	$54.6512	$54.65	$54.65	$54.70
Purchase #7	$86.45	13.402%	$98.036	$98.04	$98.05	$98.00
7 purchase totals =	$801.28		$880.5504	$880.56	$880.60	$880.50