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	13.443%	$16.8917	$16.89	$16.90	$16.90
Purchase #2	$28.69	4.321%	$29.9297	$29.93	$29.95	$29.90
Purchase #3	$106.66	9.181%	$116.4525	$116.45	$116.45	$116.50
Purchase #4	$192.53	3.806%	$199.8577	$199.86	$199.85	$199.90
Purchase #5	$161.35	7.869%	$174.0466	$174.05	$174.05	$174.00
Purchase #6	$227.95	12.266%	$255.9103	$255.91	$255.90	$255.90
Purchase #7	$92.73	8.274%	$100.4025	$100.40	$100.40	$100.40
7 purchase totals =	$824.80		$893.4910	$893.49	$893.50	$893.50