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	$78.37	8.307%	$84.8802	$84.88	$84.90	$84.90
Purchase #2	$244.96	4.146%	$255.116	$255.12	$255.10	$255.10
Purchase #3	$158.90	9.698%	$174.3101	$174.31	$174.30	$174.30
Purchase #4	$245.37	10.531%	$271.2099	$271.21	$271.20	$271.20
Purchase #5	$91.59	7.586%	$98.538	$98.54	$98.55	$98.50
Purchase #6	$46.39	13.356%	$52.5858	$52.59	$52.60	$52.60
Purchase #7	$132.76	12.371%	$149.1837	$149.18	$149.20	$149.20
7 purchase totals =	$998.34		$1,085.8237	$1,085.83	$1,085.85	$1,085.80