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	$139.31	13.774%	$158.4986	$158.50	$158.50	$158.50
Purchase #2	$112.92	9.653%	$123.8202	$123.82	$123.80	$123.80
Purchase #3	$198.76	6.219%	$211.1209	$211.12	$211.10	$211.10
Purchase #4	$66.30	12.857%	$74.8242	$74.82	$74.80	$74.80
Purchase #5	$35.32	11.528%	$39.3917	$39.39	$39.40	$39.40
Purchase #6	$101.94	6.534%	$108.6008	$108.60	$108.60	$108.60
Purchase #7	$72.38	7.241%	$77.621	$77.62	$77.60	$77.60
7 purchase totals =	$726.93		$793.8774	$793.87	$793.80	$793.80