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	$17.64	9.274%	$19.2759	$19.28	$19.30	$19.30
Purchase #2	$94.79	6.145%	$100.6148	$100.61	$100.60	$100.60
Purchase #3	$125.75	7.276%	$134.8996	$134.90	$134.90	$134.90
Purchase #4	$111.62	5.538%	$117.8015	$117.80	$117.80	$117.80
Purchase #5	$77.51	11.588%	$86.4919	$86.49	$86.50	$86.50
Purchase #6	$31.40	5.305%	$33.0658	$33.07	$33.05	$33.10
Purchase #7	$16.93	9.329%	$18.5094	$18.51	$18.50	$18.50
7 purchase totals =	$475.64		$510.6589	$510.66	$510.65	$510.70