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	$40.68	8.689%	$44.2147	$44.21	$44.20	$44.20
Purchase #2	$6.53	5.549%	$6.8923	$6.89	$6.90	$6.90
Purchase #3	$35.85	13.214%	$40.5872	$40.59	$40.60	$40.60
Purchase #4	$24.32	12.853%	$27.4458	$27.45	$27.45	$27.40
Purchase #5	$90.66	12.192%	$101.7133	$101.71	$101.70	$101.70
Purchase #6	$59.35	7.725%	$63.9348	$63.93	$63.95	$63.90
Purchase #7	$97.81	6.860%	$104.5198	$104.52	$104.50	$104.50
7 purchase totals =	$355.20		$389.3079	$389.30	$389.30	$389.20