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	$28.46	4.548%	$29.7544	$29.75	$29.75	$29.80
Purchase #2	$45.61	9.506%	$49.9457	$49.95	$49.95	$49.90
Purchase #3	$163.25	11.754%	$182.4384	$182.44	$182.45	$182.40
Purchase #4	$59.83	11.573%	$66.7541	$66.75	$66.75	$66.80
Purchase #5	$27.78	6.189%	$29.4993	$29.50	$29.50	$29.50
Purchase #6	$80.51	12.425%	$90.5134	$90.51	$90.50	$90.50
Purchase #7	$108.58	7.280%	$116.4846	$116.48	$116.50	$116.50
7 purchase totals =	$514.02		$565.3899	$565.38	$565.40	$565.40