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	$156.28	10.580%	$172.8144	$172.81	$172.80	$172.80
Purchase #2	$230.85	5.330%	$243.1543	$243.15	$243.15	$243.20
Purchase #3	$9.46	7.270%	$10.1477	$10.15	$10.15	$10.10
Purchase #4	$131.87	9.774%	$144.759	$144.76	$144.75	$144.80
Purchase #5	$45.56	7.382%	$48.9232	$48.92	$48.90	$48.90
Purchase #6	$45.34	13.846%	$51.6178	$51.62	$51.60	$51.60
Purchase #7	$69.78	12.864%	$78.7565	$78.76	$78.75	$78.80
7 purchase totals =	$689.14		$750.1729	$750.17	$750.10	$750.20