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	$101.35	11.343%	$112.8461	$112.85	$112.85	$112.80
Purchase #2	$240.77	12.204%	$270.1536	$270.15	$270.15	$270.20
Purchase #3	$123.83	6.860%	$132.3247	$132.32	$132.30	$132.30
Purchase #4	$173.65	4.543%	$181.5389	$181.54	$181.55	$181.50
Purchase #5	$231.71	4.235%	$241.5229	$241.52	$241.50	$241.50
Purchase #6	$232.25	6.605%	$247.5901	$247.59	$247.60	$247.60
Purchase #7	$108.98	8.763%	$118.5299	$118.53	$118.55	$118.50
7 purchase totals =	$1,212.54		$1,304.5062	$1,304.50	$1,304.50	$1,304.40