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	$14.89	8.624%	$16.1741	$16.17	$16.15	$16.20
Purchase #2	$73.29	4.363%	$76.4876	$76.49	$76.50	$76.50
Purchase #3	$86.57	11.500%	$96.5256	$96.53	$96.55	$96.50
Purchase #4	$24.85	10.535%	$27.4679	$27.47	$27.45	$27.50
Purchase #5	$84.69	5.403%	$89.2658	$89.27	$89.25	$89.30
Purchase #6	$30.81	6.623%	$32.8505	$32.85	$32.85	$32.90
Purchase #7	$80.47	9.391%	$88.0269	$88.03	$88.05	$88.00
7 purchase totals =	$395.57		$426.7984	$426.81	$426.80	$426.90