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	$170.74	4.799%	$178.9338	$178.93	$178.95	$178.90
Purchase #2	$52.95	11.531%	$59.0557	$59.06	$59.05	$59.10
Purchase #3	$100.81	10.352%	$111.2459	$111.25	$111.25	$111.20
Purchase #4	$114.32	12.233%	$128.3048	$128.30	$128.30	$128.30
Purchase #5	$9.40	4.809%	$9.852	$9.85	$9.85	$9.90
Purchase #6	$32.26	9.731%	$35.3992	$35.40	$35.40	$35.40
Purchase #7	$138.99	5.638%	$146.8263	$146.83	$146.85	$146.80
7 purchase totals =	$619.47		$669.6177	$669.62	$669.65	$669.60