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	$157.59	5.508%	$166.2701	$166.27	$166.25	$166.30
Purchase #2	$136.98	4.669%	$143.3756	$143.38	$143.40	$143.40
Purchase #3	$90.93	12.808%	$102.5763	$102.58	$102.60	$102.60
Purchase #4	$207.76	10.229%	$229.0118	$229.01	$229.00	$229.00
Purchase #5	$19.49	11.779%	$21.7857	$21.79	$21.80	$21.80
Purchase #6	$72.53	3.292%	$74.9177	$74.92	$74.90	$74.90
Purchase #7	$56.69	4.842%	$59.4349	$59.43	$59.45	$59.40
7 purchase totals =	$741.97		$797.3721	$797.38	$797.40	$797.40