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	$42.56	6.535%	$45.3413	$45.34	$45.35	$45.30
Purchase #2	$237.43	5.231%	$249.85	$249.85	$249.85	$249.90
Purchase #3	$7.88	11.345%	$8.774	$8.77	$8.75	$8.80
Purchase #4	$62.88	4.156%	$65.4933	$65.49	$65.50	$65.50
Purchase #5	$38.47	13.868%	$43.805	$43.81	$43.80	$43.80
Purchase #6	$46.62	11.136%	$51.8116	$51.81	$51.80	$51.80
Purchase #7	$116.92	9.313%	$127.8088	$127.81	$127.80	$127.80
7 purchase totals =	$552.76		$592.8840	$592.88	$592.85	$592.90