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	$9.64	11.681%	$10.766	$10.77	$10.75	$10.80
Purchase #2	$84.31	6.327%	$89.6443	$89.64	$89.65	$89.60
Purchase #3	$74.51	8.401%	$80.7696	$80.77	$80.75	$80.80
Purchase #4	$216.96	7.857%	$234.0065	$234.01	$234.00	$234.00
Purchase #5	$86.44	6.223%	$91.8192	$91.82	$91.80	$91.80
Purchase #6	$48.99	4.665%	$51.2754	$51.28	$51.30	$51.30
Purchase #7	$160.27	4.340%	$167.2257	$167.23	$167.25	$167.20
7 purchase totals =	$681.12		$725.5067	$725.52	$725.50	$725.50