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	$132.67	11.492%	$147.9164	$147.92	$147.90	$147.90
Purchase #2	$173.47	5.288%	$182.6431	$182.64	$182.65	$182.60
Purchase #3	$31.35	5.851%	$33.1843	$33.18	$33.20	$33.20
Purchase #4	$207.93	10.863%	$230.5174	$230.52	$230.50	$230.50
Purchase #5	$64.28	3.638%	$66.6185	$66.62	$66.60	$66.60
Purchase #6	$54.54	8.187%	$59.0052	$59.01	$59.00	$59.00
Purchase #7	$19.65	6.471%	$20.9216	$20.92	$20.90	$20.90
7 purchase totals =	$683.89		$740.8065	$740.81	$740.75	$740.70