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	$75.28	7.151%	$80.6633	$80.66	$80.65	$80.70
Purchase #2	$111.27	12.534%	$125.2166	$125.22	$125.20	$125.20
Purchase #3	$24.88	11.622%	$27.7716	$27.77	$27.75	$27.80
Purchase #4	$152.49	10.354%	$168.2788	$168.28	$168.30	$168.30
Purchase #5	$108.96	13.117%	$123.2523	$123.25	$123.25	$123.30
Purchase #6	$157.98	9.160%	$172.451	$172.45	$172.45	$172.50
Purchase #7	$40.35	5.621%	$42.6181	$42.62	$42.60	$42.60
7 purchase totals =	$671.21		$740.2517	$740.25	$740.20	$740.40