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	$68.89	5.639%	$72.7747	$72.77	$72.75	$72.80
Purchase #2	$136.52	7.838%	$147.2204	$147.22	$147.20	$147.20
Purchase #3	$106.63	9.145%	$116.3813	$116.38	$116.40	$116.40
Purchase #4	$126.99	9.697%	$139.3042	$139.30	$139.30	$139.30
Purchase #5	$130.81	10.551%	$144.6118	$144.61	$144.60	$144.60
Purchase #6	$136.95	4.592%	$143.2387	$143.24	$143.25	$143.20
Purchase #7	$72.78	11.740%	$81.3244	$81.32	$81.30	$81.30
7 purchase totals =	$779.57		$844.8555	$844.84	$844.80	$844.80