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	$34.30	7.358%	$36.8238	$36.82	$36.80	$36.80
Purchase #2	$40.82	5.227%	$42.9537	$42.95	$42.95	$43.00
Purchase #3	$175.32	6.451%	$186.6299	$186.63	$186.65	$186.60
Purchase #4	$231.73	13.736%	$263.5604	$263.56	$263.55	$263.60
Purchase #5	$103.96	13.243%	$117.7274	$117.73	$117.75	$117.70
Purchase #6	$68.53	6.384%	$72.905	$72.91	$72.90	$72.90
Purchase #7	$52.81	3.799%	$54.8163	$54.82	$54.80	$54.80
7 purchase totals =	$707.47		$775.4165	$775.42	$775.40	$775.40