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	$40.91	3.601%	$42.3832	$42.38	$42.40	$42.40
Purchase #2	$112.94	11.746%	$126.2059	$126.21	$126.20	$126.20
Purchase #3	$248.43	12.175%	$278.6764	$278.68	$278.70	$278.70
Purchase #4	$237.98	6.755%	$254.0555	$254.06	$254.05	$254.10
Purchase #5	$103.83	7.355%	$111.4667	$111.47	$111.45	$111.50
Purchase #6	$26.59	4.676%	$27.8333	$27.83	$27.85	$27.80
Purchase #7	$175.45	13.210%	$198.6269	$198.63	$198.65	$198.60
7 purchase totals =	$946.13		$1,039.2479	$1,039.26	$1,039.30	$1,039.30