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	$183.87	12.485%	$206.8262	$206.83	$206.85	$206.80
Purchase #2	$108.30	7.309%	$116.2156	$116.22	$116.20	$116.20
Purchase #3	$110.53	11.401%	$123.1315	$123.13	$123.15	$123.10
Purchase #4	$82.92	10.488%	$91.6166	$91.62	$91.60	$91.60
Purchase #5	$58.84	11.274%	$65.4736	$65.47	$65.45	$65.50
Purchase #6	$206.38	5.717%	$218.1787	$218.18	$218.20	$218.20
Purchase #7	$36.83	3.334%	$38.0579	$38.06	$38.05	$38.10
7 purchase totals =	$787.67		$859.5001	$859.51	$859.50	$859.50