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	$45.56	4.635%	$47.6717	$47.67	$47.65	$47.70
Purchase #2	$227.75	8.409%	$246.9015	$246.90	$246.90	$246.90
Purchase #3	$231.81	10.263%	$255.6007	$255.60	$255.60	$255.60
Purchase #4	$80.80	12.183%	$90.6439	$90.64	$90.65	$90.60
Purchase #5	$105.73	13.299%	$119.791	$119.79	$119.80	$119.80
Purchase #6	$202.32	12.263%	$227.1305	$227.13	$227.15	$227.10
Purchase #7	$13.47	12.661%	$15.1754	$15.18	$15.20	$15.20
7 purchase totals =	$907.44		$1,002.9147	$1,002.91	$1,002.95	$1,002.90