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	$138.65	12.804%	$156.4027	$156.40	$156.40	$156.40
Purchase #2	$167.60	8.240%	$181.4102	$181.41	$181.40	$181.40
Purchase #3	$241.33	3.553%	$249.9045	$249.90	$249.90	$249.90
Purchase #4	$207.64	11.669%	$231.8695	$231.87	$231.85	$231.90
Purchase #5	$216.78	5.456%	$228.6075	$228.61	$228.60	$228.60
Purchase #6	$248.79	6.850%	$265.8321	$265.83	$265.85	$265.80
Purchase #7	$179.40	3.335%	$185.383	$185.38	$185.40	$185.40
7 purchase totals =	$1,400.19		$1,499.4095	$1,499.40	$1,499.40	$1,499.40