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	$218.72	3.849%	$227.1385	$227.14	$227.15	$227.10
Purchase #2	$28.77	8.144%	$31.113	$31.11	$31.10	$31.10
Purchase #3	$16.37	3.371%	$16.9218	$16.92	$16.90	$16.90
Purchase #4	$137.77	11.268%	$153.2939	$153.29	$153.30	$153.30
Purchase #5	$131.30	4.534%	$137.2531	$137.25	$137.25	$137.30
Purchase #6	$46.81	4.388%	$48.864	$48.86	$48.85	$48.90
Purchase #7	$60.83	8.121%	$65.77	$65.77	$65.75	$65.80
7 purchase totals =	$640.57		$680.3543	$680.34	$680.30	$680.40