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	$48.29	8.339%	$52.3169	$52.32	$52.30	$52.30
Purchase #2	$42.60	5.677%	$45.0184	$45.02	$45.00	$45.00
Purchase #3	$162.34	11.286%	$180.6617	$180.66	$180.65	$180.70
Purchase #4	$154.88	10.503%	$171.147	$171.15	$171.15	$171.10
Purchase #5	$96.75	3.865%	$100.4894	$100.49	$100.50	$100.50
Purchase #6	$21.25	13.193%	$24.0535	$24.05	$24.05	$24.10
Purchase #7	$102.43	10.376%	$113.0581	$113.06	$113.05	$113.10
7 purchase totals =	$628.54		$686.7450	$686.75	$686.70	$686.80