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	$189.45	8.446%	$205.4509	$205.45	$205.45	$205.50
Purchase #2	$247.43	12.719%	$278.9006	$278.90	$278.90	$278.90
Purchase #3	$126.87	4.437%	$132.4992	$132.50	$132.50	$132.50
Purchase #4	$219.76	10.782%	$243.4545	$243.45	$243.45	$243.50
Purchase #5	$157.79	9.307%	$172.4755	$172.48	$172.50	$172.50
Purchase #6	$248.33	11.150%	$276.0188	$276.02	$276.00	$276.00
Purchase #7	$217.76	5.571%	$229.8914	$229.89	$229.90	$229.90
7 purchase totals =	$1,407.39		$1,538.6909	$1,538.69	$1,538.70	$1,538.80