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	$113.41	6.299%	$120.5537	$120.55	$120.55	$120.60
Purchase #2	$188.51	4.157%	$196.3464	$196.35	$196.35	$196.30
Purchase #3	$246.99	13.361%	$279.9903	$279.99	$280.00	$280.00
Purchase #4	$203.41	9.479%	$222.6912	$222.69	$222.70	$222.70
Purchase #5	$71.99	9.392%	$78.7513	$78.75	$78.75	$78.80
Purchase #6	$133.91	8.150%	$144.8237	$144.82	$144.80	$144.80
Purchase #7	$62.86	7.277%	$67.4343	$67.43	$67.45	$67.40
7 purchase totals =	$1,021.08		$1,110.5909	$1,110.58	$1,110.60	$1,110.60