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	$52.64	12.690%	$59.32	$59.32	$59.30	$59.30
Purchase #2	$73.56	11.346%	$81.9061	$81.91	$81.90	$81.90
Purchase #3	$18.68	13.314%	$21.1671	$21.17	$21.15	$21.20
Purchase #4	$119.85	5.164%	$126.0391	$126.04	$126.05	$126.00
Purchase #5	$48.59	11.493%	$54.1744	$54.17	$54.15	$54.20
Purchase #6	$159.71	9.293%	$174.5519	$174.55	$174.55	$174.60
Purchase #7	$37.56	3.681%	$38.9426	$38.94	$38.95	$38.90
7 purchase totals =	$510.59		$556.1012	$556.10	$556.05	$556.10