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	$36.63	7.472%	$39.367	$39.37	$39.35	$39.40
Purchase #2	$166.61	4.602%	$174.2774	$174.28	$174.30	$174.30
Purchase #3	$179.98	9.427%	$196.9467	$196.95	$196.95	$196.90
Purchase #4	$63.36	6.196%	$67.2858	$67.29	$67.30	$67.30
Purchase #5	$245.99	12.193%	$275.9836	$275.98	$276.00	$276.00
Purchase #6	$58.43	13.853%	$66.5243	$66.52	$66.50	$66.50
Purchase #7	$134.36	7.559%	$144.5163	$144.52	$144.50	$144.50
7 purchase totals =	$885.36		$964.9011	$964.91	$964.90	$964.90