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	$170.92	11.197%	$190.0579	$190.06	$190.05	$190.10
Purchase #2	$56.83	11.570%	$63.4052	$63.41	$63.40	$63.40
Purchase #3	$136.73	6.711%	$145.906	$145.91	$145.90	$145.90
Purchase #4	$122.41	4.839%	$128.3334	$128.33	$128.35	$128.30
Purchase #5	$58.91	6.361%	$62.6573	$62.66	$62.65	$62.70
Purchase #6	$19.37	5.451%	$20.4259	$20.43	$20.45	$20.40
Purchase #7	$51.46	5.440%	$54.2594	$54.26	$54.25	$54.30
7 purchase totals =	$616.63		$665.0451	$665.06	$665.05	$665.10