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	$96.94	4.704%	$101.5001	$101.50	$101.50	$101.50
Purchase #2	$33.43	12.222%	$37.5158	$37.52	$37.50	$37.50
Purchase #3	$132.27	5.744%	$139.8676	$139.87	$139.85	$139.90
Purchase #4	$35.77	5.562%	$37.7595	$37.76	$37.75	$37.80
Purchase #5	$45.85	13.102%	$51.8573	$51.86	$51.85	$51.90
Purchase #6	$117.45	13.771%	$133.624	$133.62	$133.60	$133.60
Purchase #7	$113.36	5.316%	$119.3862	$119.39	$119.40	$119.40
7 purchase totals =	$575.07		$621.5105	$621.52	$621.45	$621.60