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	$74.85	4.507%	$78.2235	$78.22	$78.20	$78.20
Purchase #2	$70.86	5.294%	$74.6113	$74.61	$74.60	$74.60
Purchase #3	$100.82	13.782%	$114.715	$114.72	$114.70	$114.70
Purchase #4	$143.50	4.491%	$149.9446	$149.94	$149.95	$149.90
Purchase #5	$90.78	12.492%	$102.1202	$102.12	$102.10	$102.10
Purchase #6	$64.98	11.534%	$72.4748	$72.47	$72.45	$72.50
Purchase #7	$211.88	7.595%	$227.9723	$227.97	$227.95	$228.00
7 purchase totals =	$757.67		$820.0617	$820.05	$819.95	$820.00