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	$76.90	4.779%	$80.5751	$80.58	$80.60	$80.60
Purchase #2	$71.53	8.536%	$77.6358	$77.64	$77.65	$77.60
Purchase #3	$244.42	6.789%	$261.0137	$261.01	$261.00	$261.00
Purchase #4	$63.34	7.291%	$67.9581	$67.96	$67.95	$68.00
Purchase #5	$82.55	8.459%	$89.5329	$89.53	$89.55	$89.50
Purchase #6	$46.55	11.759%	$52.0238	$52.02	$52.00	$52.00
Purchase #7	$11.88	4.367%	$12.3988	$12.40	$12.40	$12.40
7 purchase totals =	$597.17		$641.1382	$641.14	$641.15	$641.10