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	$119.86	13.486%	$136.0243	$136.02	$136.00	$136.00
Purchase #2	$205.90	4.609%	$215.3899	$215.39	$215.40	$215.40
Purchase #3	$80.47	6.373%	$85.5984	$85.60	$85.60	$85.60
Purchase #4	$74.87	4.466%	$78.2137	$78.21	$78.20	$78.20
Purchase #5	$149.94	4.574%	$156.7983	$156.80	$156.80	$156.80
Purchase #6	$80.80	7.265%	$86.6701	$86.67	$86.65	$86.70
Purchase #7	$169.56	12.180%	$190.2124	$190.21	$190.20	$190.20
7 purchase totals =	$881.40		$948.9071	$948.90	$948.85	$948.90