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	$26.37	11.554%	$29.4168	$29.42	$29.40	$29.40
Purchase #2	$176.86	11.327%	$196.8929	$196.89	$196.90	$196.90
Purchase #3	$198.51	12.709%	$223.7386	$223.74	$223.75	$223.70
Purchase #4	$131.71	5.169%	$138.5181	$138.52	$138.50	$138.50
Purchase #5	$87.95	11.848%	$98.3703	$98.37	$98.35	$98.40
Purchase #6	$46.40	3.133%	$47.8537	$47.85	$47.85	$47.90
Purchase #7	$29.51	7.666%	$31.7722	$31.77	$31.75	$31.80
7 purchase totals =	$697.31		$766.5626	$766.56	$766.50	$766.60