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	$114.97	12.182%	$128.9756	$128.98	$129.00	$129.00
Purchase #2	$68.47	5.667%	$72.3502	$72.35	$72.35	$72.40
Purchase #3	$27.67	12.145%	$31.0305	$31.03	$31.05	$31.00
Purchase #4	$164.78	11.607%	$183.906	$183.91	$183.90	$183.90
Purchase #5	$29.38	11.449%	$32.7437	$32.74	$32.75	$32.70
Purchase #6	$146.60	10.652%	$162.2158	$162.22	$162.20	$162.20
Purchase #7	$112.50	5.149%	$118.2926	$118.29	$118.30	$118.30
7 purchase totals =	$664.37		$729.5144	$729.52	$729.55	$729.50