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	$19.33	13.663%	$21.9711	$21.97	$21.95	$22.00
Purchase #2	$196.35	3.805%	$203.8211	$203.82	$203.80	$203.80
Purchase #3	$92.41	13.680%	$105.0517	$105.05	$105.05	$105.10
Purchase #4	$94.31	12.275%	$105.8866	$105.89	$105.90	$105.90
Purchase #5	$74.56	3.329%	$77.0421	$77.04	$77.05	$77.00
Purchase #6	$96.95	5.845%	$102.6167	$102.62	$102.60	$102.60
Purchase #7	$222.85	9.205%	$243.3633	$243.36	$243.35	$243.40
7 purchase totals =	$796.76		$859.7526	$859.75	$859.70	$859.80