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	$234.99	6.430%	$250.0999	$250.10	$250.10	$250.10
Purchase #2	$230.80	11.578%	$257.522	$257.52	$257.50	$257.50
Purchase #3	$18.68	6.805%	$19.9512	$19.95	$19.95	$20.00
Purchase #4	$106.61	11.404%	$118.7678	$118.77	$118.75	$118.80
Purchase #5	$92.85	8.704%	$100.9317	$100.93	$100.95	$100.90
Purchase #6	$199.41	8.268%	$215.8972	$215.90	$215.90	$215.90
Purchase #7	$54.68	3.371%	$56.5233	$56.52	$56.50	$56.50
7 purchase totals =	$938.02		$1,019.6931	$1,019.69	$1,019.65	$1,019.70