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	$128.86	12.112%	$144.4675	$144.47	$144.45	$144.50
Purchase #2	$131.96	10.185%	$145.4001	$145.40	$145.40	$145.40
Purchase #3	$98.48	12.196%	$110.4906	$110.49	$110.50	$110.50
Purchase #4	$100.60	13.534%	$114.2152	$114.22	$114.20	$114.20
Purchase #5	$238.87	4.444%	$249.4854	$249.49	$249.50	$249.50
Purchase #6	$200.79	12.578%	$226.0454	$226.05	$226.05	$226.00
Purchase #7	$35.75	8.472%	$38.7787	$38.78	$38.80	$38.80
7 purchase totals =	$935.31		$1,028.8829	$1,028.90	$1,028.90	$1,028.90