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	$115.52	13.402%	$131.002	$131.00	$131.00	$131.00
Purchase #2	$145.63	4.687%	$152.4557	$152.46	$152.45	$152.50
Purchase #3	$50.47	4.615%	$52.7992	$52.80	$52.80	$52.80
Purchase #4	$157.89	11.218%	$175.6021	$175.60	$175.60	$175.60
Purchase #5	$32.50	10.191%	$35.8121	$35.81	$35.80	$35.80
Purchase #6	$30.44	8.607%	$33.06	$33.06	$33.05	$33.10
Purchase #7	$164.32	7.420%	$176.5125	$176.51	$176.50	$176.50
7 purchase totals =	$696.77		$757.2436	$757.24	$757.20	$757.30