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	$225.88	6.825%	$241.2963	$241.30	$241.30	$241.30
Purchase #2	$54.60	13.342%	$61.8847	$61.88	$61.90	$61.90
Purchase #3	$229.63	8.294%	$248.6755	$248.68	$248.70	$248.70
Purchase #4	$105.60	5.753%	$111.6752	$111.68	$111.70	$111.70
Purchase #5	$249.81	9.196%	$272.7825	$272.78	$272.80	$272.80
Purchase #6	$29.89	13.310%	$33.8684	$33.87	$33.85	$33.90
Purchase #7	$67.25	3.673%	$69.7201	$69.72	$69.70	$69.70
7 purchase totals =	$962.66		$1,039.9027	$1,039.91	$1,039.95	$1,040.00