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	$224.52	3.108%	$231.4981	$231.50	$231.50	$231.50
Purchase #2	$61.41	8.821%	$66.827	$66.83	$66.85	$66.80
Purchase #3	$67.34	13.479%	$76.4168	$76.42	$76.40	$76.40
Purchase #4	$163.78	3.154%	$168.9456	$168.95	$168.95	$168.90
Purchase #5	$108.31	4.521%	$113.2067	$113.21	$113.20	$113.20
Purchase #6	$19.38	10.649%	$21.4438	$21.44	$21.45	$21.40
Purchase #7	$179.96	9.180%	$196.4803	$196.48	$196.50	$196.50
7 purchase totals =	$824.70		$874.8183	$874.83	$874.85	$874.70