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	$170.83	8.588%	$185.5009	$185.50	$185.50	$185.50
Purchase #2	$126.94	6.781%	$135.5478	$135.55	$135.55	$135.50
Purchase #3	$111.86	11.627%	$124.866	$124.87	$124.85	$124.90
Purchase #4	$22.94	11.561%	$25.5921	$25.59	$25.60	$25.60
Purchase #5	$108.93	13.870%	$124.0386	$124.04	$124.05	$124.00
Purchase #6	$73.46	6.754%	$78.4215	$78.42	$78.40	$78.40
Purchase #7	$243.81	6.274%	$259.1066	$259.11	$259.10	$259.10
7 purchase totals =	$858.77		$933.0735	$933.08	$933.05	$933.00