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	$228.34	13.588%	$259.3668	$259.37	$259.35	$259.40
Purchase #2	$64.71	6.724%	$69.0611	$69.06	$69.05	$69.10
Purchase #3	$159.83	12.418%	$179.6777	$179.68	$179.70	$179.70
Purchase #4	$35.43	5.589%	$37.4102	$37.41	$37.40	$37.40
Purchase #5	$195.42	12.145%	$219.1538	$219.15	$219.15	$219.20
Purchase #6	$146.37	3.645%	$151.7052	$151.71	$151.70	$151.70
Purchase #7	$213.32	9.629%	$233.8606	$233.86	$233.85	$233.90
7 purchase totals =	$1,043.42		$1,150.2354	$1,150.24	$1,150.20	$1,150.40