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	$243.68	12.132%	$273.2433	$273.24	$273.25	$273.20
Purchase #2	$114.80	12.317%	$128.9399	$128.94	$128.95	$128.90
Purchase #3	$222.89	13.778%	$253.5998	$253.60	$253.60	$253.60
Purchase #4	$49.44	10.282%	$54.5234	$54.52	$54.50	$54.50
Purchase #5	$50.27	8.511%	$54.5485	$54.55	$54.55	$54.50
Purchase #6	$241.27	3.388%	$249.4442	$249.44	$249.45	$249.40
Purchase #7	$247.97	7.699%	$267.0612	$267.06	$267.05	$267.10
7 purchase totals =	$1,170.32		$1,281.3603	$1,281.35	$1,281.35	$1,281.20