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	$15.69	5.472%	$16.5486	$16.55	$16.55	$16.50
Purchase #2	$70.54	13.245%	$79.883	$79.88	$79.90	$79.90
Purchase #3	$40.30	8.520%	$43.7336	$43.73	$43.75	$43.70
Purchase #4	$217.96	3.640%	$225.8937	$225.89	$225.90	$225.90
Purchase #5	$167.25	4.510%	$174.793	$174.79	$174.80	$174.80
Purchase #6	$124.96	11.610%	$139.4679	$139.47	$139.45	$139.50
Purchase #7	$240.44	9.160%	$262.4643	$262.46	$262.45	$262.50
7 purchase totals =	$877.14		$942.7841	$942.77	$942.80	$942.80