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	$12.47	4.296%	$13.0057	$13.01	$13.00	$13.00
Purchase #2	$54.35	9.798%	$59.6752	$59.68	$59.70	$59.70
Purchase #3	$139.38	13.537%	$158.2479	$158.25	$158.25	$158.20
Purchase #4	$162.55	5.544%	$171.5618	$171.56	$171.55	$171.60
Purchase #5	$128.44	11.452%	$143.1489	$143.15	$143.15	$143.10
Purchase #6	$54.80	12.190%	$61.4801	$61.48	$61.50	$61.50
Purchase #7	$108.29	9.411%	$118.4812	$118.48	$118.50	$118.50
7 purchase totals =	$660.28		$725.6008	$725.61	$725.65	$725.60