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	$160.30	12.109%	$179.7107	$179.71	$179.70	$179.70
Purchase #2	$115.61	9.660%	$126.7779	$126.78	$126.80	$126.80
Purchase #3	$21.90	13.249%	$24.8015	$24.80	$24.80	$24.80
Purchase #4	$94.92	5.623%	$100.2574	$100.26	$100.25	$100.30
Purchase #5	$54.64	3.780%	$56.7054	$56.71	$56.70	$56.70
Purchase #6	$54.51	5.705%	$57.6198	$57.62	$57.60	$57.60
Purchase #7	$109.56	10.667%	$121.2468	$121.25	$121.25	$121.20
7 purchase totals =	$611.44		$667.1195	$667.13	$667.10	$667.10