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	$114.26	8.188%	$123.6156	$123.62	$123.60	$123.60
Purchase #2	$115.98	10.575%	$128.2449	$128.24	$128.25	$128.20
Purchase #3	$150.26	11.693%	$167.8299	$167.83	$167.85	$167.80
Purchase #4	$61.53	7.122%	$65.9122	$65.91	$65.90	$65.90
Purchase #5	$127.32	5.272%	$134.0323	$134.03	$134.05	$134.00
Purchase #6	$114.69	7.380%	$123.1541	$123.15	$123.15	$123.20
Purchase #7	$42.73	11.655%	$47.7102	$47.71	$47.70	$47.70
7 purchase totals =	$726.77		$790.4992	$790.49	$790.50	$790.40