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	$39.60	13.255%	$44.849	$44.85	$44.85	$44.80
Purchase #2	$78.48	13.678%	$89.2145	$89.21	$89.20	$89.20
Purchase #3	$18.71	11.617%	$20.8835	$20.88	$20.90	$20.90
Purchase #4	$206.94	12.619%	$233.0538	$233.05	$233.05	$233.10
Purchase #5	$135.35	6.286%	$143.8581	$143.86	$143.85	$143.90
Purchase #6	$218.81	10.347%	$241.4503	$241.45	$241.45	$241.50
Purchase #7	$69.39	4.462%	$72.4862	$72.49	$72.50	$72.50
7 purchase totals =	$767.28		$845.7954	$845.79	$845.80	$845.90