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	$158.63	6.129%	$168.3524	$168.35	$168.35	$168.40
Purchase #2	$173.36	13.273%	$196.3701	$196.37	$196.35	$196.40
Purchase #3	$178.74	6.503%	$190.3635	$190.36	$190.35	$190.40
Purchase #4	$60.85	11.114%	$67.6129	$67.61	$67.60	$67.60
Purchase #5	$32.28	6.623%	$34.4179	$34.42	$34.40	$34.40
Purchase #6	$105.84	5.500%	$111.6612	$111.66	$111.65	$111.70
Purchase #7	$203.95	8.758%	$221.8119	$221.81	$221.80	$221.80
7 purchase totals =	$913.65		$990.5899	$990.58	$990.50	$990.70