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	$117.98	13.134%	$133.4755	$133.48	$133.50	$133.50
Purchase #2	$108.44	9.165%	$118.3785	$118.38	$118.40	$118.40
Purchase #3	$75.85	9.247%	$82.8638	$82.86	$82.85	$82.90
Purchase #4	$64.69	12.252%	$72.6158	$72.62	$72.60	$72.60
Purchase #5	$37.31	5.282%	$39.2807	$39.28	$39.30	$39.30
Purchase #6	$133.83	9.126%	$146.0433	$146.04	$146.05	$146.00
Purchase #7	$189.59	4.380%	$197.894	$197.89	$197.90	$197.90
7 purchase totals =	$727.69		$790.5516	$790.55	$790.60	$790.60