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	$244.29	11.625%	$272.6887	$272.69	$272.70	$272.70
Purchase #2	$16.31	12.758%	$18.3908	$18.39	$18.40	$18.40
Purchase #3	$186.85	12.673%	$210.5295	$210.53	$210.55	$210.50
Purchase #4	$72.81	3.852%	$75.6146	$75.61	$75.60	$75.60
Purchase #5	$90.36	8.200%	$97.7695	$97.77	$97.75	$97.80
Purchase #6	$40.89	12.392%	$45.9571	$45.96	$45.95	$46.00
Purchase #7	$91.81	8.523%	$99.635	$99.64	$99.65	$99.60
7 purchase totals =	$743.32		$820.5852	$820.59	$820.60	$820.60