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	$16.27	12.168%	$18.2497	$18.25	$18.25	$18.20
Purchase #2	$231.73	5.458%	$244.3778	$244.38	$244.40	$244.40
Purchase #3	$215.60	11.510%	$240.4156	$240.42	$240.40	$240.40
Purchase #4	$219.59	4.288%	$229.006	$229.01	$229.00	$229.00
Purchase #5	$124.37	6.437%	$132.3757	$132.38	$132.40	$132.40
Purchase #6	$174.80	3.485%	$180.8918	$180.89	$180.90	$180.90
Purchase #7	$51.56	9.523%	$56.4701	$56.47	$56.45	$56.50
7 purchase totals =	$1,033.92		$1,101.7867	$1,101.80	$1,101.80	$1,101.80