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	$138.51	4.106%	$144.1972	$144.20	$144.20	$144.20
Purchase #2	$138.80	3.337%	$143.4318	$143.43	$143.45	$143.40
Purchase #3	$105.64	7.405%	$113.4626	$113.46	$113.45	$113.50
Purchase #4	$49.83	11.800%	$55.7099	$55.71	$55.70	$55.70
Purchase #5	$85.86	4.196%	$89.4627	$89.46	$89.45	$89.50
Purchase #6	$70.79	6.601%	$75.4628	$75.46	$75.45	$75.50
Purchase #7	$28.87	3.782%	$29.9619	$29.96	$29.95	$30.00
7 purchase totals =	$618.30		$651.6889	$651.68	$651.65	$651.80