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	$17.50	12.837%	$19.7465	$19.75	$19.75	$19.70
Purchase #2	$212.37	5.550%	$224.1565	$224.16	$224.15	$224.20
Purchase #3	$139.69	8.737%	$151.8947	$151.89	$151.90	$151.90
Purchase #4	$229.25	11.332%	$255.2286	$255.23	$255.25	$255.20
Purchase #5	$235.28	6.210%	$249.8909	$249.89	$249.90	$249.90
Purchase #6	$61.69	9.157%	$67.339	$67.34	$67.35	$67.30
Purchase #7	$93.79	10.388%	$103.5329	$103.53	$103.55	$103.50
7 purchase totals =	$989.57		$1,071.7891	$1,071.79	$1,071.85	$1,071.70