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	$171.54	6.826%	$183.2493	$183.25	$183.25	$183.20
Purchase #2	$26.94	10.666%	$29.8134	$29.81	$29.80	$29.80
Purchase #3	$155.28	12.183%	$174.1978	$174.20	$174.20	$174.20
Purchase #4	$33.68	11.668%	$37.6098	$37.61	$37.60	$37.60
Purchase #5	$16.89	12.167%	$18.945	$18.95	$18.95	$18.90
Purchase #6	$136.83	6.173%	$145.2765	$145.28	$145.30	$145.30
Purchase #7	$248.85	10.636%	$275.3177	$275.32	$275.30	$275.30
7 purchase totals =	$790.01		$864.4095	$864.42	$864.40	$864.30