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	$210.81	13.181%	$238.5969	$238.60	$238.60	$238.60
Purchase #2	$124.27	3.122%	$128.1497	$128.15	$128.15	$128.10
Purchase #3	$35.37	9.389%	$38.6909	$38.69	$38.70	$38.70
Purchase #4	$12.98	10.463%	$14.3381	$14.34	$14.35	$14.30
Purchase #5	$113.90	4.222%	$118.7089	$118.71	$118.70	$118.70
Purchase #6	$226.38	3.746%	$234.8602	$234.86	$234.85	$234.90
Purchase #7	$106.86	12.172%	$119.867	$119.87	$119.85	$119.90
7 purchase totals =	$830.57		$893.2117	$893.22	$893.20	$893.20