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	$50.27	12.789%	$56.699	$56.70	$56.70	$56.70
Purchase #2	$80.86	12.291%	$90.7985	$90.80	$90.80	$90.80
Purchase #3	$141.56	6.378%	$150.5887	$150.59	$150.60	$150.60
Purchase #4	$135.34	7.214%	$145.1034	$145.10	$145.10	$145.10
Purchase #5	$193.90	6.589%	$206.6761	$206.68	$206.70	$206.70
Purchase #6	$133.51	4.584%	$139.6301	$139.63	$139.65	$139.60
Purchase #7	$6.71	9.852%	$7.3711	$7.37	$7.35	$7.40
7 purchase totals =	$742.15		$796.8669	$796.87	$796.90	$796.90