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	$83.38	7.742%	$89.8353	$89.84	$89.85	$89.80
Purchase #2	$245.47	11.772%	$274.3667	$274.37	$274.35	$274.40
Purchase #3	$219.29	11.528%	$244.5698	$244.57	$244.55	$244.60
Purchase #4	$64.47	4.495%	$67.3679	$67.37	$67.35	$67.40
Purchase #5	$197.30	8.195%	$213.4687	$213.47	$213.45	$213.50
Purchase #6	$129.97	12.635%	$146.3917	$146.39	$146.40	$146.40
Purchase #7	$57.37	9.248%	$62.6756	$62.68	$62.70	$62.70
7 purchase totals =	$997.25		$1,098.6757	$1,098.69	$1,098.65	$1,098.80