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	$126.72	7.829%	$136.6409	$136.64	$136.65	$136.60
Purchase #2	$245.45	6.649%	$261.77	$261.77	$261.75	$261.80
Purchase #3	$214.81	6.371%	$228.4955	$228.50	$228.50	$228.50
Purchase #4	$12.46	10.371%	$13.7522	$13.75	$13.75	$13.80
Purchase #5	$196.52	13.128%	$222.3191	$222.32	$222.30	$222.30
Purchase #6	$245.98	8.710%	$267.4049	$267.40	$267.40	$267.40
Purchase #7	$249.62	12.187%	$280.0412	$280.04	$280.05	$280.00
7 purchase totals =	$1,291.56		$1,410.4238	$1,410.42	$1,410.40	$1,410.40