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	$19.99	3.558%	$20.7012	$20.70	$20.70	$20.70
Purchase #2	$86.32	10.724%	$95.577	$95.58	$95.60	$95.60
Purchase #3	$195.45	13.767%	$222.3576	$222.36	$222.35	$222.40
Purchase #4	$77.56	10.328%	$85.5704	$85.57	$85.55	$85.60
Purchase #5	$140.94	7.758%	$151.8741	$151.87	$151.85	$151.90
Purchase #6	$67.90	7.675%	$73.1113	$73.11	$73.10	$73.10
Purchase #7	$82.46	6.550%	$87.8611	$87.86	$87.85	$87.90
7 purchase totals =	$670.62		$737.0527	$737.05	$737.00	$737.20