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	$86.32	4.604%	$90.2942	$90.29	$90.30	$90.30
Purchase #2	$207.58	9.461%	$227.2191	$227.22	$227.20	$227.20
Purchase #3	$12.90	12.127%	$14.4644	$14.46	$14.45	$14.50
Purchase #4	$11.84	11.469%	$13.1979	$13.20	$13.20	$13.20
Purchase #5	$146.82	3.635%	$152.1569	$152.16	$152.15	$152.20
Purchase #6	$38.82	11.577%	$43.3142	$43.31	$43.30	$43.30
Purchase #7	$174.76	8.616%	$189.8173	$189.82	$189.80	$189.80
7 purchase totals =	$679.04		$730.4640	$730.46	$730.40	$730.50