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	$243.50	9.863%	$267.5164	$267.52	$267.50	$267.50
Purchase #2	$51.97	6.397%	$55.2945	$55.29	$55.30	$55.30
Purchase #3	$201.56	11.551%	$224.8422	$224.84	$224.85	$224.80
Purchase #4	$210.45	5.607%	$222.2499	$222.25	$222.25	$222.20
Purchase #5	$95.31	13.530%	$108.2054	$108.21	$108.20	$108.20
Purchase #6	$236.87	10.861%	$262.5965	$262.60	$262.60	$262.60
Purchase #7	$146.46	9.155%	$159.8684	$159.87	$159.85	$159.90
7 purchase totals =	$1,186.12		$1,300.5733	$1,300.58	$1,300.55	$1,300.50