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	$31.75	6.859%	$33.9277	$33.93	$33.95	$33.90
Purchase #2	$234.97	8.594%	$255.1633	$255.16	$255.15	$255.20
Purchase #3	$69.34	3.290%	$71.6213	$71.62	$71.60	$71.60
Purchase #4	$50.37	8.848%	$54.8267	$54.83	$54.85	$54.80
Purchase #5	$38.71	6.804%	$41.3438	$41.34	$41.35	$41.30
Purchase #6	$50.72	9.372%	$55.4735	$55.47	$55.45	$55.50
Purchase #7	$45.50	7.318%	$48.8297	$48.83	$48.85	$48.80
7 purchase totals =	$521.36		$561.1860	$561.18	$561.20	$561.10