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	$16.27	6.175%	$17.2747	$17.27	$17.25	$17.30
Purchase #2	$226.48	10.468%	$250.1879	$250.19	$250.20	$250.20
Purchase #3	$54.61	3.541%	$56.5437	$56.54	$56.55	$56.50
Purchase #4	$31.33	7.149%	$33.5698	$33.57	$33.55	$33.60
Purchase #5	$229.38	13.538%	$260.4335	$260.43	$260.45	$260.40
Purchase #6	$84.26	7.657%	$90.7118	$90.71	$90.70	$90.70
Purchase #7	$94.50	7.389%	$101.4826	$101.48	$101.50	$101.50
7 purchase totals =	$736.83		$810.2040	$810.19	$810.20	$810.20