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	$141.89	4.670%	$148.5163	$148.52	$148.50	$148.50
Purchase #2	$144.57	12.434%	$162.5458	$162.55	$162.55	$162.50
Purchase #3	$169.36	6.159%	$179.7909	$179.79	$179.80	$179.80
Purchase #4	$16.65	7.704%	$17.9327	$17.93	$17.95	$17.90
Purchase #5	$230.66	8.768%	$250.8843	$250.88	$250.90	$250.90
Purchase #6	$178.75	6.576%	$190.5046	$190.50	$190.50	$190.50
Purchase #7	$105.52	13.414%	$119.6745	$119.67	$119.65	$119.70
7 purchase totals =	$987.40		$1,069.8491	$1,069.84	$1,069.85	$1,069.80