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	$31.50	6.856%	$33.6596	$33.66	$33.65	$33.70
Purchase #2	$87.87	13.343%	$99.5945	$99.59	$99.60	$99.60
Purchase #3	$117.29	6.236%	$124.6042	$124.60	$124.60	$124.60
Purchase #4	$67.27	13.305%	$76.2203	$76.22	$76.20	$76.20
Purchase #5	$114.49	4.272%	$119.381	$119.38	$119.40	$119.40
Purchase #6	$39.89	7.729%	$42.9731	$42.97	$42.95	$43.00
Purchase #7	$83.82	10.388%	$92.5272	$92.53	$92.55	$92.50
7 purchase totals =	$542.13		$588.9599	$588.95	$588.95	$589.00