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	$113.39	5.353%	$119.4598	$119.46	$119.45	$119.50
Purchase #2	$109.59	10.327%	$120.9074	$120.91	$120.90	$120.90
Purchase #3	$107.66	3.555%	$111.4873	$111.49	$111.50	$111.50
Purchase #4	$89.31	3.617%	$92.5403	$92.54	$92.55	$92.50
Purchase #5	$57.56	3.671%	$59.673	$59.67	$59.65	$59.70
Purchase #6	$211.77	7.584%	$227.8306	$227.83	$227.85	$227.80
Purchase #7	$225.49	4.702%	$236.0925	$236.09	$236.10	$236.10
7 purchase totals =	$914.77		$967.9909	$967.99	$968.00	$968.00