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	$31.57	8.274%	$34.1821	$34.18	$34.20	$34.20
Purchase #2	$179.42	9.608%	$196.6587	$196.66	$196.65	$196.70
Purchase #3	$184.44	13.600%	$209.5238	$209.52	$209.50	$209.50
Purchase #4	$234.92	8.682%	$255.3158	$255.32	$255.30	$255.30
Purchase #5	$92.47	4.754%	$96.866	$96.87	$96.85	$96.90
Purchase #6	$77.89	4.649%	$81.5111	$81.51	$81.50	$81.50
Purchase #7	$105.42	3.372%	$108.9748	$108.97	$108.95	$109.00
7 purchase totals =	$906.13		$983.0323	$983.03	$982.95	$983.10