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	$206.44	6.211%	$219.262	$219.26	$219.25	$219.30
Purchase #2	$234.57	11.427%	$261.3743	$261.37	$261.35	$261.40
Purchase #3	$155.37	10.811%	$172.1671	$172.17	$172.15	$172.20
Purchase #4	$6.72	13.643%	$7.6368	$7.64	$7.65	$7.60
Purchase #5	$73.66	10.728%	$81.5622	$81.56	$81.55	$81.60
Purchase #6	$90.42	5.238%	$95.1562	$95.16	$95.15	$95.20
Purchase #7	$29.64	8.704%	$32.2199	$32.22	$32.20	$32.20
7 purchase totals =	$796.82		$869.3785	$869.38	$869.30	$869.50