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	$53.76	10.826%	$59.5801	$59.58	$59.60	$59.60
Purchase #2	$245.98	11.303%	$273.7831	$273.78	$273.80	$273.80
Purchase #3	$30.48	9.825%	$33.4747	$33.47	$33.45	$33.50
Purchase #4	$18.39	3.356%	$19.0072	$19.01	$19.00	$19.00
Purchase #5	$95.29	6.862%	$101.8288	$101.83	$101.85	$101.80
Purchase #6	$208.32	10.850%	$230.9227	$230.92	$230.90	$230.90
Purchase #7	$73.79	13.583%	$83.8129	$83.81	$83.80	$83.80
7 purchase totals =	$726.01		$802.4095	$802.40	$802.40	$802.40