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	$20.31	9.390%	$22.2171	$22.22	$22.20	$22.20
Purchase #2	$94.53	5.354%	$99.5911	$99.59	$99.60	$99.60
Purchase #3	$243.62	5.234%	$256.3711	$256.37	$256.35	$256.40
Purchase #4	$84.49	7.222%	$90.5919	$90.59	$90.60	$90.60
Purchase #5	$145.56	5.861%	$154.0913	$154.09	$154.10	$154.10
Purchase #6	$207.96	4.316%	$216.9356	$216.94	$216.95	$216.90
Purchase #7	$77.28	3.207%	$79.7584	$79.76	$79.75	$79.80
7 purchase totals =	$873.75		$919.5565	$919.56	$919.55	$919.60