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	$65.96	10.173%	$72.6701	$72.67	$72.65	$72.70
Purchase #2	$99.99	7.794%	$107.7832	$107.78	$107.80	$107.80
Purchase #3	$213.71	7.870%	$230.529	$230.53	$230.55	$230.50
Purchase #4	$78.36	12.553%	$88.1965	$88.20	$88.20	$88.20
Purchase #5	$119.46	10.776%	$132.333	$132.33	$132.35	$132.30
Purchase #6	$107.96	3.617%	$111.8649	$111.86	$111.85	$111.90
Purchase #7	$244.46	6.520%	$260.3988	$260.40	$260.40	$260.40
7 purchase totals =	$929.90		$1,003.7755	$1,003.77	$1,003.80	$1,003.80