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	$71.81	12.111%	$80.5069	$80.51	$80.50	$80.50
Purchase #2	$40.76	4.285%	$42.5066	$42.51	$42.50	$42.50
Purchase #3	$189.57	12.137%	$212.5781	$212.58	$212.60	$212.60
Purchase #4	$86.52	10.262%	$95.3987	$95.40	$95.40	$95.40
Purchase #5	$37.74	10.248%	$41.6076	$41.61	$41.60	$41.60
Purchase #6	$228.81	5.108%	$240.4976	$240.50	$240.50	$240.50
Purchase #7	$15.44	13.853%	$17.5789	$17.58	$17.60	$17.60
7 purchase totals =	$670.65		$730.6744	$730.69	$730.70	$730.70