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	$153.85	12.185%	$172.5966	$172.60	$172.60	$172.60
Purchase #2	$121.40	12.517%	$136.5956	$136.60	$136.60	$136.60
Purchase #3	$142.34	10.339%	$157.0565	$157.06	$157.05	$157.10
Purchase #4	$65.76	6.600%	$70.1002	$70.10	$70.10	$70.10
Purchase #5	$41.26	10.156%	$45.4504	$45.45	$45.45	$45.50
Purchase #6	$91.39	9.772%	$100.3206	$100.32	$100.30	$100.30
Purchase #7	$80.85	12.701%	$91.1188	$91.12	$91.10	$91.10
7 purchase totals =	$696.85		$773.2387	$773.25	$773.20	$773.30