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	$13.83	8.566%	$15.0147	$15.01	$15.00	$15.00
Purchase #2	$246.26	3.555%	$255.0145	$255.01	$255.00	$255.00
Purchase #3	$130.43	5.533%	$137.6467	$137.65	$137.65	$137.60
Purchase #4	$61.57	10.335%	$67.9333	$67.93	$67.95	$67.90
Purchase #5	$149.85	4.389%	$156.4269	$156.43	$156.45	$156.40
Purchase #6	$78.69	11.646%	$87.8542	$87.85	$87.85	$87.90
Purchase #7	$233.34	4.353%	$243.4973	$243.50	$243.50	$243.50
7 purchase totals =	$913.97		$963.3876	$963.38	$963.40	$963.30