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	$20.70	5.738%	$21.8878	$21.89	$21.90	$21.90
Purchase #2	$99.34	12.602%	$111.8588	$111.86	$111.85	$111.90
Purchase #3	$215.37	11.525%	$240.1914	$240.19	$240.20	$240.20
Purchase #4	$54.26	12.781%	$61.195	$61.20	$61.20	$61.20
Purchase #5	$231.74	7.405%	$248.9003	$248.90	$248.90	$248.90
Purchase #6	$48.66	10.320%	$53.6817	$53.68	$53.70	$53.70
Purchase #7	$5.35	7.846%	$5.7698	$5.77	$5.75	$5.80
7 purchase totals =	$675.42		$743.4848	$743.49	$743.50	$743.60