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	$157.70	7.416%	$169.395	$169.40	$169.40	$169.40
Purchase #2	$59.44	11.626%	$66.3505	$66.35	$66.35	$66.40
Purchase #3	$94.60	6.194%	$100.4595	$100.46	$100.45	$100.50
Purchase #4	$238.78	8.367%	$258.7587	$258.76	$258.75	$258.80
Purchase #5	$31.76	3.436%	$32.8513	$32.85	$32.85	$32.90
Purchase #6	$123.44	13.384%	$139.9612	$139.96	$139.95	$140.00
Purchase #7	$163.33	6.297%	$173.6149	$173.61	$173.60	$173.60
7 purchase totals =	$869.05		$941.3911	$941.39	$941.35	$941.60