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	$39.72	9.345%	$43.4318	$43.43	$43.45	$43.40
Purchase #2	$71.75	11.336%	$79.8836	$79.88	$79.90	$79.90
Purchase #3	$64.65	4.418%	$67.5062	$67.51	$67.50	$67.50
Purchase #4	$128.74	11.149%	$143.0932	$143.09	$143.10	$143.10
Purchase #5	$184.48	11.595%	$205.8705	$205.87	$205.85	$205.90
Purchase #6	$150.95	12.225%	$169.4036	$169.40	$169.40	$169.40
Purchase #7	$198.49	9.774%	$217.8904	$217.89	$217.90	$217.90
7 purchase totals =	$838.78		$927.0793	$927.07	$927.10	$927.10