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	$137.83	13.451%	$156.3695	$156.37	$156.35	$156.40
Purchase #2	$109.86	6.511%	$117.013	$117.01	$117.00	$117.00
Purchase #3	$242.90	10.238%	$267.7681	$267.77	$267.75	$267.80
Purchase #4	$237.86	10.405%	$262.6093	$262.61	$262.60	$262.60
Purchase #5	$163.99	9.684%	$179.8708	$179.87	$179.85	$179.90
Purchase #6	$148.26	11.624%	$165.4937	$165.49	$165.50	$165.50
Purchase #7	$240.91	8.659%	$261.7704	$261.77	$261.75	$261.80
7 purchase totals =	$1,281.61		$1,410.8948	$1,410.89	$1,410.80	$1,411.00