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	$223.44	10.169%	$246.1616	$246.16	$246.15	$246.20
Purchase #2	$186.85	5.245%	$196.6503	$196.65	$196.65	$196.70
Purchase #3	$82.35	5.147%	$86.5886	$86.59	$86.60	$86.60
Purchase #4	$11.97	12.535%	$13.4704	$13.47	$13.45	$13.50
Purchase #5	$147.44	3.499%	$152.5989	$152.60	$152.60	$152.60
Purchase #6	$86.77	13.344%	$98.3486	$98.35	$98.35	$98.30
Purchase #7	$171.96	8.831%	$187.1458	$187.15	$187.15	$187.10
7 purchase totals =	$910.78		$980.9642	$980.97	$980.95	$981.00