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	$98.72	3.455%	$102.1308	$102.13	$102.15	$102.10
Purchase #2	$120.65	5.165%	$126.8816	$126.88	$126.90	$126.90
Purchase #3	$149.39	13.499%	$169.5562	$169.56	$169.55	$169.60
Purchase #4	$10.98	12.845%	$12.3904	$12.39	$12.40	$12.40
Purchase #5	$120.93	5.256%	$127.2861	$127.29	$127.30	$127.30
Purchase #6	$78.97	9.677%	$86.6119	$86.61	$86.60	$86.60
Purchase #7	$174.58	8.864%	$190.0548	$190.05	$190.05	$190.10
7 purchase totals =	$754.22		$814.9118	$814.91	$814.95	$815.00