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	$136.75	10.260%	$150.7806	$150.78	$150.80	$150.80
Purchase #2	$24.32	10.731%	$26.9298	$26.93	$26.95	$26.90
Purchase #3	$65.56	8.160%	$70.9097	$70.91	$70.90	$70.90
Purchase #4	$46.98	13.761%	$53.4449	$53.44	$53.45	$53.40
Purchase #5	$47.32	11.513%	$52.768	$52.77	$52.75	$52.80
Purchase #6	$140.74	12.208%	$157.9215	$157.92	$157.90	$157.90
Purchase #7	$18.25	8.725%	$19.8423	$19.84	$19.85	$19.80
7 purchase totals =	$479.92		$532.5968	$532.59	$532.60	$532.50