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	$23.45	3.221%	$24.2053	$24.21	$24.20	$24.20
Purchase #2	$35.32	10.829%	$39.1448	$39.14	$39.15	$39.10
Purchase #3	$65.44	10.606%	$72.3806	$72.38	$72.40	$72.40
Purchase #4	$57.38	3.567%	$59.4267	$59.43	$59.45	$59.40
Purchase #5	$169.38	3.856%	$175.9113	$175.91	$175.90	$175.90
Purchase #6	$164.32	10.683%	$181.8743	$181.87	$181.85	$181.90
Purchase #7	$16.69	3.653%	$17.2997	$17.30	$17.30	$17.30
7 purchase totals =	$531.98		$570.2427	$570.24	$570.25	$570.20