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	$37.46	3.216%	$38.6647	$38.66	$38.65	$38.70
Purchase #2	$229.59	11.140%	$255.1663	$255.17	$255.15	$255.20
Purchase #3	$200.47	4.391%	$209.2726	$209.27	$209.25	$209.30
Purchase #4	$134.44	8.215%	$145.4842	$145.48	$145.50	$145.50
Purchase #5	$25.98	6.182%	$27.5861	$27.59	$27.60	$27.60
Purchase #6	$103.78	9.549%	$113.69	$113.69	$113.70	$113.70
Purchase #7	$159.61	6.245%	$169.5776	$169.58	$169.60	$169.60
7 purchase totals =	$891.33		$959.4415	$959.44	$959.45	$959.60