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	$16.82	9.804%	$18.469	$18.47	$18.45	$18.50
Purchase #2	$207.57	5.465%	$218.9137	$218.91	$218.90	$218.90
Purchase #3	$55.38	8.180%	$59.9101	$59.91	$59.90	$59.90
Purchase #4	$55.52	6.317%	$59.0272	$59.03	$59.05	$59.00
Purchase #5	$35.74	13.160%	$40.4434	$40.44	$40.45	$40.40
Purchase #6	$16.82	5.217%	$17.6975	$17.70	$17.70	$17.70
Purchase #7	$46.59	12.546%	$52.4352	$52.44	$52.45	$52.40
7 purchase totals =	$434.44		$466.8961	$466.90	$466.90	$466.80