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	$103.27	13.761%	$117.481	$117.48	$117.50	$117.50
Purchase #2	$137.76	4.248%	$143.612	$143.61	$143.60	$143.60
Purchase #3	$33.86	12.137%	$37.9696	$37.97	$37.95	$38.00
Purchase #4	$245.43	12.346%	$275.7308	$275.73	$275.75	$275.70
Purchase #5	$154.41	9.145%	$168.5308	$168.53	$168.55	$168.50
Purchase #6	$63.58	4.108%	$66.1919	$66.19	$66.20	$66.20
Purchase #7	$13.75	12.276%	$15.438	$15.44	$15.45	$15.40
7 purchase totals =	$752.06		$824.9541	$824.95	$825.00	$824.90