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	$46.76	9.433%	$51.1709	$51.17	$51.15	$51.20
Purchase #2	$142.81	10.868%	$158.3306	$158.33	$158.35	$158.30
Purchase #3	$79.56	11.765%	$88.9202	$88.92	$88.90	$88.90
Purchase #4	$177.48	11.697%	$198.2398	$198.24	$198.25	$198.20
Purchase #5	$119.55	6.255%	$127.0279	$127.03	$127.05	$127.00
Purchase #6	$147.32	13.774%	$167.6119	$167.61	$167.60	$167.60
Purchase #7	$238.96	8.822%	$260.0411	$260.04	$260.05	$260.00
7 purchase totals =	$952.44		$1,051.3424	$1,051.34	$1,051.35	$1,051.20