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	$173.89	3.407%	$179.8144	$179.81	$179.80	$179.80
Purchase #2	$77.89	11.444%	$86.8037	$86.80	$86.80	$86.80
Purchase #3	$36.32	5.791%	$38.4233	$38.42	$38.40	$38.40
Purchase #4	$157.90	9.740%	$173.2795	$173.28	$173.30	$173.30
Purchase #5	$6.64	12.306%	$7.4571	$7.46	$7.45	$7.50
Purchase #6	$50.86	11.110%	$56.5105	$56.51	$56.50	$56.50
Purchase #7	$194.67	9.864%	$213.8722	$213.87	$213.85	$213.90
7 purchase totals =	$698.17		$756.1607	$756.15	$756.10	$756.20