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	$66.27	6.105%	$70.3158	$70.32	$70.30	$70.30
Purchase #2	$125.95	11.524%	$140.4645	$140.46	$140.45	$140.50
Purchase #3	$110.80	6.817%	$118.3532	$118.35	$118.35	$118.40
Purchase #4	$56.65	12.551%	$63.7601	$63.76	$63.75	$63.80
Purchase #5	$43.84	4.296%	$45.7234	$45.72	$45.70	$45.70
Purchase #6	$134.28	4.569%	$140.4153	$140.42	$140.40	$140.40
Purchase #7	$78.73	9.508%	$86.2156	$86.22	$86.20	$86.20
7 purchase totals =	$616.52		$665.2479	$665.25	$665.15	$665.30