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	$8.31	13.866%	$9.4623	$9.46	$9.45	$9.50
Purchase #2	$82.59	9.520%	$90.4526	$90.45	$90.45	$90.50
Purchase #3	$163.47	7.317%	$175.4311	$175.43	$175.45	$175.40
Purchase #4	$67.92	11.539%	$75.7573	$75.76	$75.75	$75.80
Purchase #5	$174.57	12.531%	$196.4454	$196.45	$196.45	$196.40
Purchase #6	$198.52	13.694%	$225.7053	$225.71	$225.70	$225.70
Purchase #7	$182.57	11.336%	$203.2661	$203.27	$203.25	$203.30
7 purchase totals =	$877.95		$976.5201	$976.53	$976.50	$976.60