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	$84.77	5.516%	$89.4459	$89.45	$89.45	$89.40
Purchase #2	$32.75	11.868%	$36.6368	$36.64	$36.65	$36.60
Purchase #3	$227.29	8.789%	$247.2665	$247.27	$247.25	$247.30
Purchase #4	$146.35	13.862%	$166.637	$166.64	$166.65	$166.60
Purchase #5	$37.29	9.687%	$40.9023	$40.90	$40.90	$40.90
Purchase #6	$136.42	5.579%	$144.0309	$144.03	$144.05	$144.00
Purchase #7	$145.44	6.423%	$154.7816	$154.78	$154.80	$154.80
7 purchase totals =	$810.31		$879.7010	$879.71	$879.75	$879.60