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	$190.81	6.517%	$203.2451	$203.25	$203.25	$203.20
Purchase #2	$37.59	7.834%	$40.5348	$40.53	$40.55	$40.50
Purchase #3	$54.62	4.358%	$57.0003	$57.00	$57.00	$57.00
Purchase #4	$160.68	13.523%	$182.4088	$182.41	$182.40	$182.40
Purchase #5	$250.46	11.858%	$280.1595	$280.16	$280.15	$280.20
Purchase #6	$181.87	9.345%	$198.8658	$198.87	$198.85	$198.90
Purchase #7	$169.84	12.778%	$191.5422	$191.54	$191.55	$191.50
7 purchase totals =	$1,045.87		$1,153.7565	$1,153.76	$1,153.75	$1,153.70