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	$93.99	12.245%	$105.4991	$105.50	$105.50	$105.50
Purchase #2	$47.52	9.139%	$51.8629	$51.86	$51.85	$51.90
Purchase #3	$214.93	3.330%	$222.0872	$222.09	$222.10	$222.10
Purchase #4	$218.27	7.467%	$234.5682	$234.57	$234.55	$234.60
Purchase #5	$125.25	10.199%	$138.0242	$138.02	$138.00	$138.00
Purchase #6	$60.58	11.404%	$67.4885	$67.49	$67.50	$67.50
Purchase #7	$152.82	11.178%	$169.9022	$169.90	$169.90	$169.90
7 purchase totals =	$913.36		$989.4323	$989.43	$989.40	$989.50