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	$225.39	3.734%	$233.8061	$233.81	$233.80	$233.80
Purchase #2	$118.49	12.147%	$132.883	$132.88	$132.90	$132.90
Purchase #3	$6.63	6.248%	$7.0442	$7.04	$7.05	$7.00
Purchase #4	$44.86	9.466%	$49.1064	$49.11	$49.10	$49.10
Purchase #5	$25.79	5.577%	$27.2283	$27.23	$27.25	$27.20
Purchase #6	$38.34	9.671%	$42.0479	$42.05	$42.05	$42.00
Purchase #7	$205.56	8.418%	$222.864	$222.86	$222.85	$222.90
7 purchase totals =	$665.06		$714.9799	$714.98	$715.00	$714.90