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	$18.77	13.545%	$21.3124	$21.31	$21.30	$21.30
Purchase #2	$92.95	4.766%	$97.38	$97.38	$97.40	$97.40
Purchase #3	$55.38	11.112%	$61.5338	$61.53	$61.55	$61.50
Purchase #4	$79.82	11.610%	$89.0871	$89.09	$89.10	$89.10
Purchase #5	$241.93	4.785%	$253.5064	$253.51	$253.50	$253.50
Purchase #6	$143.49	5.657%	$151.6072	$151.61	$151.60	$151.60
Purchase #7	$215.59	12.295%	$242.0968	$242.10	$242.10	$242.10
7 purchase totals =	$847.93		$916.5237	$916.53	$916.55	$916.50