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	$81.80	9.747%	$89.773	$89.77	$89.75	$89.80
Purchase #2	$82.62	9.865%	$90.7705	$90.77	$90.75	$90.80
Purchase #3	$134.73	9.140%	$147.0443	$147.04	$147.05	$147.00
Purchase #4	$11.91	12.326%	$13.378	$13.38	$13.40	$13.40
Purchase #5	$68.59	13.856%	$78.0938	$78.09	$78.10	$78.10
Purchase #6	$25.30	7.246%	$27.1332	$27.13	$27.15	$27.10
Purchase #7	$105.47	3.119%	$108.7596	$108.76	$108.75	$108.80
7 purchase totals =	$510.42		$554.9524	$554.94	$554.95	$555.00