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	$27.77	3.795%	$28.8239	$28.82	$28.80	$28.80
Purchase #2	$13.96	13.452%	$15.8379	$15.84	$15.85	$15.80
Purchase #3	$39.67	7.376%	$42.5961	$42.60	$42.60	$42.60
Purchase #4	$130.83	11.227%	$145.5183	$145.52	$145.50	$145.50
Purchase #5	$187.79	12.241%	$210.7774	$210.78	$210.80	$210.80
Purchase #6	$171.89	9.213%	$187.7262	$187.73	$187.75	$187.70
Purchase #7	$108.76	4.714%	$113.8869	$113.89	$113.90	$113.90
7 purchase totals =	$680.67		$745.1667	$745.18	$745.20	$745.10