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	$75.70	3.706%	$78.5054	$78.51	$78.50	$78.50
Purchase #2	$18.25	4.517%	$19.0744	$19.07	$19.05	$19.10
Purchase #3	$250.46	3.205%	$258.4872	$258.49	$258.50	$258.50
Purchase #4	$195.67	12.145%	$219.4341	$219.43	$219.45	$219.40
Purchase #5	$65.80	10.460%	$72.6827	$72.68	$72.70	$72.70
Purchase #6	$58.47	13.706%	$66.4839	$66.48	$66.50	$66.50
Purchase #7	$249.64	4.367%	$260.5418	$260.54	$260.55	$260.50
7 purchase totals =	$913.99		$975.2095	$975.20	$975.25	$975.20