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	$17.59	12.808%	$19.8429	$19.84	$19.85	$19.80
Purchase #2	$34.88	6.722%	$37.2246	$37.22	$37.20	$37.20
Purchase #3	$92.81	13.415%	$105.2605	$105.26	$105.25	$105.30
Purchase #4	$79.60	9.696%	$87.318	$87.32	$87.30	$87.30
Purchase #5	$183.31	4.164%	$190.943	$190.94	$190.95	$190.90
Purchase #6	$82.60	4.411%	$86.2435	$86.24	$86.25	$86.20
Purchase #7	$129.74	6.316%	$137.9344	$137.93	$137.95	$137.90
7 purchase totals =	$620.53		$664.7669	$664.75	$664.75	$664.60