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	$236.42	9.266%	$258.3267	$258.33	$258.35	$258.30
Purchase #2	$136.81	3.453%	$141.534	$141.53	$141.55	$141.50
Purchase #3	$215.31	12.207%	$241.5929	$241.59	$241.60	$241.60
Purchase #4	$46.56	10.345%	$51.3766	$51.38	$51.40	$51.40
Purchase #5	$49.63	10.709%	$54.9449	$54.94	$54.95	$54.90
Purchase #6	$52.53	8.818%	$57.1621	$57.16	$57.15	$57.20
Purchase #7	$75.52	5.328%	$79.5437	$79.54	$79.55	$79.50
7 purchase totals =	$812.78		$884.4809	$884.47	$884.55	$884.40