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	$226.48	9.686%	$248.4169	$248.42	$248.40	$248.40
Purchase #2	$66.79	8.131%	$72.2207	$72.22	$72.20	$72.20
Purchase #3	$204.82	9.508%	$224.2943	$224.29	$224.30	$224.30
Purchase #4	$132.76	10.176%	$146.2697	$146.27	$146.25	$146.30
Purchase #5	$98.71	13.167%	$111.7071	$111.71	$111.70	$111.70
Purchase #6	$196.55	13.196%	$222.4867	$222.49	$222.50	$222.50
Purchase #7	$247.28	8.234%	$267.641	$267.64	$267.65	$267.60
7 purchase totals =	$1,173.39		$1,293.0364	$1,293.04	$1,293.00	$1,293.00