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	$138.38	10.657%	$153.1272	$153.13	$153.15	$153.10
Purchase #2	$191.88	4.381%	$200.2863	$200.29	$200.30	$200.30
Purchase #3	$42.85	5.542%	$45.2247	$45.22	$45.20	$45.20
Purchase #4	$214.78	13.449%	$243.6658	$243.67	$243.65	$243.70
Purchase #5	$73.75	12.661%	$83.0875	$83.09	$83.10	$83.10
Purchase #6	$154.71	9.504%	$169.4136	$169.41	$169.40	$169.40
Purchase #7	$188.72	8.722%	$205.1802	$205.18	$205.20	$205.20
7 purchase totals =	$1,005.07		$1,099.9853	$1,099.99	$1,100.00	$1,100.00