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	$249.71	11.223%	$277.735	$277.74	$277.75	$277.70
Purchase #2	$180.77	6.549%	$192.6086	$192.61	$192.60	$192.60
Purchase #3	$141.88	10.574%	$156.8824	$156.88	$156.90	$156.90
Purchase #4	$138.69	8.802%	$150.8975	$150.90	$150.90	$150.90
Purchase #5	$146.74	6.630%	$156.4689	$156.47	$156.45	$156.50
Purchase #6	$158.81	4.462%	$165.8961	$165.90	$165.90	$165.90
Purchase #7	$34.66	11.169%	$38.5312	$38.53	$38.55	$38.50
7 purchase totals =	$1,051.26		$1,139.0197	$1,139.03	$1,139.05	$1,139.00