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	$33.83	8.178%	$36.5966	$36.60	$36.60	$36.60
Purchase #2	$116.29	6.628%	$123.9977	$124.00	$124.00	$124.00
Purchase #3	$212.39	7.593%	$228.5168	$228.52	$228.50	$228.50
Purchase #4	$82.56	3.123%	$85.1383	$85.14	$85.15	$85.10
Purchase #5	$212.59	7.296%	$228.1006	$228.10	$228.10	$228.10
Purchase #6	$29.52	13.822%	$33.6003	$33.60	$33.60	$33.60
Purchase #7	$81.88	7.863%	$88.3182	$88.32	$88.30	$88.30
7 purchase totals =	$769.06		$824.2685	$824.28	$824.25	$824.20