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	$168.78	8.844%	$183.7069	$183.71	$183.70	$183.70
Purchase #2	$36.52	12.610%	$41.1252	$41.13	$41.15	$41.10
Purchase #3	$82.92	9.225%	$90.5694	$90.57	$90.55	$90.60
Purchase #4	$61.69	3.683%	$63.962	$63.96	$63.95	$64.00
Purchase #5	$231.45	9.258%	$252.8776	$252.88	$252.90	$252.90
Purchase #6	$153.62	7.527%	$165.183	$165.18	$165.20	$165.20
Purchase #7	$53.40	10.816%	$59.1757	$59.18	$59.20	$59.20
7 purchase totals =	$788.38		$856.5998	$856.61	$856.65	$856.70