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	$145.28	3.503%	$150.3692	$150.37	$150.35	$150.40
Purchase #2	$80.97	10.389%	$89.382	$89.38	$89.40	$89.40
Purchase #3	$40.36	5.198%	$42.4579	$42.46	$42.45	$42.50
Purchase #4	$241.84	5.139%	$254.2682	$254.27	$254.25	$254.30
Purchase #5	$126.45	5.365%	$133.234	$133.23	$133.25	$133.20
Purchase #6	$6.60	10.169%	$7.2712	$7.27	$7.25	$7.30
Purchase #7	$103.75	13.405%	$117.6577	$117.66	$117.65	$117.70
7 purchase totals =	$745.25		$794.6402	$794.64	$794.60	$794.80