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	$250.77	11.712%	$280.1402	$280.14	$280.15	$280.10
Purchase #2	$108.28	10.457%	$119.6028	$119.60	$119.60	$119.60
Purchase #3	$141.97	5.368%	$149.5909	$149.59	$149.60	$149.60
Purchase #4	$19.94	12.692%	$22.4708	$22.47	$22.45	$22.50
Purchase #5	$218.95	11.851%	$244.8978	$244.90	$244.90	$244.90
Purchase #6	$85.28	11.745%	$95.2961	$95.30	$95.30	$95.30
Purchase #7	$219.85	12.130%	$246.5178	$246.52	$246.50	$246.50
7 purchase totals =	$1,045.04		$1,158.5164	$1,158.52	$1,158.50	$1,158.50