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	$68.52	6.423%	$72.921	$72.92	$72.90	$72.90
Purchase #2	$121.67	7.873%	$131.2491	$131.25	$131.25	$131.20
Purchase #3	$194.90	13.866%	$221.9248	$221.92	$221.90	$221.90
Purchase #4	$224.83	6.691%	$239.8734	$239.87	$239.85	$239.90
Purchase #5	$10.96	12.789%	$12.3617	$12.36	$12.35	$12.40
Purchase #6	$39.75	10.113%	$43.7699	$43.77	$43.75	$43.80
Purchase #7	$239.88	13.603%	$272.5109	$272.51	$272.50	$272.50
7 purchase totals =	$900.51		$994.6108	$994.60	$994.50	$994.60