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	$212.98	3.546%	$220.5323	$220.53	$220.55	$220.50
Purchase #2	$235.71	10.342%	$260.0871	$260.09	$260.10	$260.10
Purchase #3	$139.37	3.118%	$143.7156	$143.72	$143.70	$143.70
Purchase #4	$241.64	7.402%	$259.5262	$259.53	$259.55	$259.50
Purchase #5	$53.37	6.585%	$56.8844	$56.88	$56.90	$56.90
Purchase #6	$167.39	10.593%	$185.1216	$185.12	$185.10	$185.10
Purchase #7	$184.99	6.383%	$196.7979	$196.80	$196.80	$196.80
7 purchase totals =	$1,235.45		$1,322.6651	$1,322.67	$1,322.70	$1,322.60