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	$154.63	3.860%	$160.5987	$160.60	$160.60	$160.60
Purchase #2	$68.70	4.387%	$71.7139	$71.71	$71.70	$71.70
Purchase #3	$156.77	12.222%	$175.9304	$175.93	$175.95	$175.90
Purchase #4	$193.96	3.392%	$200.5391	$200.54	$200.55	$200.50
Purchase #5	$195.61	12.849%	$220.7439	$220.74	$220.75	$220.70
Purchase #6	$177.71	10.792%	$196.8885	$196.89	$196.90	$196.90
Purchase #7	$134.87	7.792%	$145.3791	$145.38	$145.40	$145.40
7 purchase totals =	$1,082.25		$1,171.7936	$1,171.79	$1,171.85	$1,171.70