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	$17.76	4.341%	$18.531	$18.53	$18.55	$18.50
Purchase #2	$102.80	8.676%	$111.7189	$111.72	$111.70	$111.70
Purchase #3	$157.63	4.397%	$164.561	$164.56	$164.55	$164.60
Purchase #4	$172.68	3.859%	$179.3437	$179.34	$179.35	$179.30
Purchase #5	$227.40	10.807%	$251.9751	$251.98	$252.00	$252.00
Purchase #6	$175.38	12.264%	$196.8886	$196.89	$196.90	$196.90
Purchase #7	$42.84	13.289%	$48.533	$48.53	$48.55	$48.50
7 purchase totals =	$896.49		$971.5513	$971.55	$971.60	$971.50