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	$26.65	3.390%	$27.5534	$27.55	$27.55	$27.60
Purchase #2	$23.67	4.375%	$24.7056	$24.71	$24.70	$24.70
Purchase #3	$72.68	6.122%	$77.1295	$77.13	$77.15	$77.10
Purchase #4	$144.43	8.248%	$156.3426	$156.34	$156.35	$156.30
Purchase #5	$78.48	13.469%	$89.0505	$89.05	$89.05	$89.10
Purchase #6	$43.52	5.843%	$46.0629	$46.06	$46.05	$46.10
Purchase #7	$28.80	8.456%	$31.2353	$31.24	$31.25	$31.20
7 purchase totals =	$418.23		$452.0798	$452.08	$452.10	$452.10