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	$45.76	11.157%	$50.8654	$50.87	$50.85	$50.90
Purchase #2	$185.86	3.596%	$192.5435	$192.54	$192.55	$192.50
Purchase #3	$166.86	11.631%	$186.2675	$186.27	$186.25	$186.30
Purchase #4	$103.44	5.708%	$109.3444	$109.34	$109.35	$109.30
Purchase #5	$82.95	9.345%	$90.7017	$90.70	$90.70	$90.70
Purchase #6	$217.63	11.849%	$243.417	$243.42	$243.40	$243.40
Purchase #7	$10.60	12.832%	$11.9602	$11.96	$11.95	$12.00
7 purchase totals =	$813.10		$885.0997	$885.10	$885.05	$885.10