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	$29.43	11.783%	$32.8977	$32.90	$32.90	$32.90
Purchase #2	$145.45	10.872%	$161.2633	$161.26	$161.25	$161.30
Purchase #3	$69.43	12.504%	$78.1115	$78.11	$78.10	$78.10
Purchase #4	$163.97	11.388%	$182.6429	$182.64	$182.65	$182.60
Purchase #5	$116.63	4.127%	$121.4433	$121.44	$121.45	$121.40
Purchase #6	$76.46	7.802%	$82.4254	$82.43	$82.45	$82.40
Purchase #7	$37.93	7.599%	$40.8123	$40.81	$40.80	$40.80
7 purchase totals =	$639.30		$699.5964	$699.59	$699.60	$699.50