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	$242.47	5.257%	$255.2166	$255.22	$255.20	$255.20
Purchase #2	$141.98	9.871%	$155.9948	$155.99	$156.00	$156.00
Purchase #3	$186.30	7.139%	$199.6	$199.60	$199.60	$199.60
Purchase #4	$106.77	6.523%	$113.7346	$113.73	$113.75	$113.70
Purchase #5	$222.64	11.704%	$248.6978	$248.70	$248.70	$248.70
Purchase #6	$49.73	7.661%	$53.5398	$53.54	$53.55	$53.50
Purchase #7	$11.83	13.822%	$13.4651	$13.47	$13.45	$13.50
7 purchase totals =	$961.72		$1,040.2487	$1,040.25	$1,040.25	$1,040.20