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	$223.25	12.554%	$251.2768	$251.28	$251.30	$251.30
Purchase #2	$15.68	13.306%	$17.7664	$17.77	$17.75	$17.80
Purchase #3	$228.58	12.394%	$256.9102	$256.91	$256.90	$256.90
Purchase #4	$112.33	9.742%	$123.2732	$123.27	$123.25	$123.30
Purchase #5	$41.89	8.624%	$45.5026	$45.50	$45.50	$45.50
Purchase #6	$165.84	6.411%	$176.472	$176.47	$176.45	$176.50
Purchase #7	$59.78	4.659%	$62.5652	$62.57	$62.55	$62.60
7 purchase totals =	$847.35		$933.7664	$933.77	$933.70	$933.90