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	$112.86	13.861%	$128.5035	$128.50	$128.50	$128.50
Purchase #2	$179.83	9.385%	$196.707	$196.71	$196.70	$196.70
Purchase #3	$59.93	12.516%	$67.4308	$67.43	$67.45	$67.40
Purchase #4	$98.33	3.664%	$101.9328	$101.93	$101.95	$101.90
Purchase #5	$136.35	10.341%	$150.45	$150.45	$150.45	$150.50
Purchase #6	$43.69	13.858%	$49.7446	$49.74	$49.75	$49.70
Purchase #7	$121.57	7.748%	$130.9892	$130.99	$131.00	$131.00
7 purchase totals =	$752.56		$825.7579	$825.75	$825.80	$825.70