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	$220.53	12.390%	$247.8537	$247.85	$247.85	$247.90
Purchase #2	$14.43	11.687%	$16.1164	$16.12	$16.10	$16.10
Purchase #3	$17.69	4.393%	$18.4671	$18.47	$18.45	$18.50
Purchase #4	$89.52	7.458%	$96.1964	$96.20	$96.20	$96.20
Purchase #5	$39.81	7.642%	$42.8523	$42.85	$42.85	$42.90
Purchase #6	$102.32	3.446%	$105.8459	$105.85	$105.85	$105.80
Purchase #7	$20.42	7.389%	$21.9288	$21.93	$21.95	$21.90
7 purchase totals =	$504.72		$549.2606	$549.27	$549.25	$549.30