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	$13.88	11.784%	$15.5156	$15.52	$15.50	$15.50
Purchase #2	$163.77	6.138%	$173.8222	$173.82	$173.80	$173.80
Purchase #3	$237.31	10.775%	$262.8802	$262.88	$262.90	$262.90
Purchase #4	$119.81	9.249%	$130.8912	$130.89	$130.90	$130.90
Purchase #5	$83.97	3.356%	$86.788	$86.79	$86.80	$86.80
Purchase #6	$101.38	11.502%	$113.0407	$113.04	$113.05	$113.00
Purchase #7	$246.40	3.681%	$255.47	$255.47	$255.45	$255.50
7 purchase totals =	$966.52		$1,038.4079	$1,038.41	$1,038.40	$1,038.40