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	$107.45	8.140%	$116.1964	$116.20	$116.20	$116.20
Purchase #2	$225.91	13.134%	$255.581	$255.58	$255.60	$255.60
Purchase #3	$71.33	5.681%	$75.3823	$75.38	$75.40	$75.40
Purchase #4	$111.90	6.827%	$119.5394	$119.54	$119.55	$119.50
Purchase #5	$86.91	4.359%	$90.6984	$90.70	$90.70	$90.70
Purchase #6	$175.40	11.863%	$196.2077	$196.21	$196.20	$196.20
Purchase #7	$113.38	5.585%	$119.7123	$119.71	$119.70	$119.70
7 purchase totals =	$892.28		$973.3175	$973.32	$973.35	$973.30