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	$92.71	10.459%	$102.4065	$102.41	$102.40	$102.40
Purchase #2	$78.63	5.276%	$82.7785	$82.78	$82.80	$82.80
Purchase #3	$47.49	10.564%	$52.5068	$52.51	$52.50	$52.50
Purchase #4	$102.37	8.450%	$111.0203	$111.02	$111.00	$111.00
Purchase #5	$83.78	8.305%	$90.7379	$90.74	$90.75	$90.70
Purchase #6	$12.89	13.243%	$14.597	$14.60	$14.60	$14.60
Purchase #7	$154.80	8.136%	$167.3945	$167.39	$167.40	$167.40
7 purchase totals =	$572.67		$621.4415	$621.45	$621.45	$621.40