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	$26.86	11.456%	$29.9371	$29.94	$29.95	$29.90
Purchase #2	$97.89	13.543%	$111.1472	$111.15	$111.15	$111.10
Purchase #3	$161.29	10.650%	$178.4674	$178.47	$178.45	$178.50
Purchase #4	$152.89	8.535%	$165.9392	$165.94	$165.95	$165.90
Purchase #5	$15.61	6.122%	$16.5656	$16.57	$16.55	$16.60
Purchase #6	$72.48	9.492%	$79.3598	$79.36	$79.35	$79.40
Purchase #7	$11.97	9.518%	$13.1093	$13.11	$13.10	$13.10
7 purchase totals =	$538.99		$594.5256	$594.54	$594.50	$594.50