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	$11.87	4.617%	$12.418	$12.42	$12.40	$12.40
Purchase #2	$89.93	10.603%	$99.4653	$99.47	$99.45	$99.50
Purchase #3	$19.84	9.235%	$21.6722	$21.67	$21.65	$21.70
Purchase #4	$36.49	5.200%	$38.3875	$38.39	$38.40	$38.40
Purchase #5	$40.33	10.661%	$44.6296	$44.63	$44.65	$44.60
Purchase #6	$154.90	9.279%	$169.2732	$169.27	$169.25	$169.30
Purchase #7	$43.57	9.299%	$47.6216	$47.62	$47.60	$47.60
7 purchase totals =	$396.93		$433.4674	$433.47	$433.40	$433.50