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	$37.78	13.789%	$42.9895	$42.99	$43.00	$43.00
Purchase #2	$157.36	6.425%	$167.4704	$167.47	$167.45	$167.50
Purchase #3	$141.59	3.417%	$146.4281	$146.43	$146.45	$146.40
Purchase #4	$100.84	8.344%	$109.2541	$109.25	$109.25	$109.30
Purchase #5	$199.61	8.707%	$216.99	$216.99	$217.00	$217.00
Purchase #6	$115.72	10.504%	$127.8752	$127.88	$127.90	$127.90
Purchase #7	$123.60	6.318%	$131.409	$131.41	$131.40	$131.40
7 purchase totals =	$876.50		$942.4163	$942.42	$942.45	$942.50