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	$24.42	10.656%	$27.0222	$27.02	$27.00	$27.00
Purchase #2	$16.72	10.463%	$18.4694	$18.47	$18.45	$18.50
Purchase #3	$247.63	11.180%	$275.315	$275.32	$275.30	$275.30
Purchase #4	$102.65	9.677%	$112.5834	$112.58	$112.60	$112.60
Purchase #5	$242.89	6.358%	$258.3329	$258.33	$258.35	$258.30
Purchase #6	$157.58	4.440%	$164.5766	$164.58	$164.60	$164.60
Purchase #7	$16.36	11.151%	$18.1843	$18.18	$18.20	$18.20
7 purchase totals =	$808.25		$874.4838	$874.48	$874.50	$874.50