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	$6.63	6.852%	$7.0843	$7.08	$7.10	$7.10
Purchase #2	$82.25	4.441%	$85.9027	$85.90	$85.90	$85.90
Purchase #3	$130.92	10.652%	$144.8656	$144.87	$144.85	$144.90
Purchase #4	$66.54	11.856%	$74.429	$74.43	$74.45	$74.40
Purchase #5	$18.47	4.234%	$19.252	$19.25	$19.25	$19.30
Purchase #6	$63.74	3.438%	$65.9314	$65.93	$65.95	$65.90
Purchase #7	$93.90	9.840%	$103.1398	$103.14	$103.15	$103.10
7 purchase totals =	$462.45		$500.6048	$500.60	$500.65	$500.60