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	$140.48	13.485%	$159.4237	$159.42	$159.40	$159.40
Purchase #2	$64.55	13.806%	$73.4618	$73.46	$73.45	$73.50
Purchase #3	$133.91	6.641%	$142.803	$142.80	$142.80	$142.80
Purchase #4	$68.54	12.331%	$76.9917	$76.99	$77.00	$77.00
Purchase #5	$215.59	8.400%	$233.6996	$233.70	$233.70	$233.70
Purchase #6	$173.78	5.829%	$183.9096	$183.91	$183.90	$183.90
Purchase #7	$248.75	12.788%	$280.5602	$280.56	$280.55	$280.60
7 purchase totals =	$1,045.60		$1,150.8496	$1,150.84	$1,150.80	$1,150.90