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	$37.38	8.374%	$40.5102	$40.51	$40.50	$40.50
Purchase #2	$16.43	6.216%	$17.4513	$17.45	$17.45	$17.50
Purchase #3	$62.87	5.760%	$66.4913	$66.49	$66.50	$66.50
Purchase #4	$174.61	8.353%	$189.1952	$189.20	$189.20	$189.20
Purchase #5	$31.50	12.548%	$35.4526	$35.45	$35.45	$35.50
Purchase #6	$93.73	6.835%	$100.1364	$100.14	$100.15	$100.10
Purchase #7	$17.50	4.394%	$18.269	$18.27	$18.25	$18.30
7 purchase totals =	$434.02		$467.5060	$467.51	$467.50	$467.60