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	$27.38	6.581%	$29.1819	$29.18	$29.20	$29.20
Purchase #2	$152.30	13.634%	$173.0646	$173.06	$173.05	$173.10
Purchase #3	$88.79	3.126%	$91.5656	$91.57	$91.55	$91.60
Purchase #4	$28.72	8.374%	$31.125	$31.13	$31.15	$31.10
Purchase #5	$16.62	9.541%	$18.2057	$18.21	$18.20	$18.20
Purchase #6	$111.38	5.134%	$117.0982	$117.10	$117.10	$117.10
Purchase #7	$153.57	9.139%	$167.6048	$167.60	$167.60	$167.60
7 purchase totals =	$578.76		$627.8458	$627.85	$627.85	$627.90