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	$213.52	4.256%	$222.6074	$222.61	$222.60	$222.60
Purchase #2	$164.98	3.361%	$170.525	$170.53	$170.55	$170.50
Purchase #3	$11.40	9.634%	$12.4983	$12.50	$12.50	$12.50
Purchase #4	$163.76	10.324%	$180.6666	$180.67	$180.65	$180.70
Purchase #5	$36.68	13.764%	$41.7286	$41.73	$41.75	$41.70
Purchase #6	$42.33	3.587%	$43.8484	$43.85	$43.85	$43.80
Purchase #7	$34.37	11.266%	$38.2421	$38.24	$38.25	$38.20
7 purchase totals =	$667.04		$710.1164	$710.13	$710.15	$710.00