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	$41.54	13.225%	$47.0337	$47.03	$47.05	$47.00
Purchase #2	$155.46	11.144%	$172.7845	$172.78	$172.80	$172.80
Purchase #3	$7.64	3.805%	$7.9307	$7.93	$7.95	$7.90
Purchase #4	$92.88	11.477%	$103.5398	$103.54	$103.55	$103.50
Purchase #5	$15.27	4.361%	$15.9359	$15.94	$15.95	$15.90
Purchase #6	$16.58	3.240%	$17.1172	$17.12	$17.10	$17.10
Purchase #7	$148.45	4.817%	$155.6008	$155.60	$155.60	$155.60
7 purchase totals =	$477.82		$519.9426	$519.94	$520.00	$519.80