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	$24.51	12.317%	$27.5289	$27.53	$27.55	$27.50
Purchase #2	$66.54	4.727%	$69.6853	$69.69	$69.70	$69.70
Purchase #3	$93.29	6.773%	$99.6085	$99.61	$99.60	$99.60
Purchase #4	$231.35	5.601%	$244.3079	$244.31	$244.30	$244.30
Purchase #5	$113.49	8.698%	$123.3614	$123.36	$123.35	$123.40
Purchase #6	$206.87	8.572%	$224.6029	$224.60	$224.60	$224.60
Purchase #7	$52.59	4.398%	$54.9029	$54.90	$54.90	$54.90
7 purchase totals =	$788.64		$843.9978	$844.00	$844.00	$844.00