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	$220.43	10.649%	$243.9036	$243.90	$243.90	$243.90
Purchase #2	$83.89	7.358%	$90.0626	$90.06	$90.05	$90.10
Purchase #3	$76.44	5.252%	$80.4546	$80.45	$80.45	$80.50
Purchase #4	$104.81	8.174%	$113.3772	$113.38	$113.40	$113.40
Purchase #5	$119.88	6.492%	$127.6626	$127.66	$127.65	$127.70
Purchase #6	$164.53	3.321%	$169.994	$169.99	$170.00	$170.00
Purchase #7	$118.74	8.300%	$128.5954	$128.60	$128.60	$128.60
7 purchase totals =	$888.72		$954.0500	$954.04	$954.05	$954.20