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	$225.98	13.336%	$256.1167	$256.12	$256.10	$256.10
Purchase #2	$161.36	9.514%	$176.7118	$176.71	$176.70	$176.70
Purchase #3	$82.72	11.222%	$92.0028	$92.00	$92.00	$92.00
Purchase #4	$137.25	9.798%	$150.6978	$150.70	$150.70	$150.70
Purchase #5	$108.30	3.731%	$112.3407	$112.34	$112.35	$112.30
Purchase #6	$195.34	5.188%	$205.4742	$205.47	$205.45	$205.50
Purchase #7	$80.80	12.118%	$90.5913	$90.59	$90.60	$90.60
7 purchase totals =	$991.75		$1,083.9353	$1,083.93	$1,083.90	$1,083.90