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	$51.98	3.866%	$53.9895	$53.99	$54.00	$54.00
Purchase #2	$190.92	3.117%	$196.871	$196.87	$196.85	$196.90
Purchase #3	$93.62	7.294%	$100.4486	$100.45	$100.45	$100.40
Purchase #4	$149.84	4.716%	$156.9065	$156.91	$156.90	$156.90
Purchase #5	$157.61	7.495%	$169.4229	$169.42	$169.40	$169.40
Purchase #6	$246.58	13.108%	$278.9017	$278.90	$278.90	$278.90
Purchase #7	$20.45	4.270%	$21.3232	$21.32	$21.30	$21.30
7 purchase totals =	$911.00		$977.8634	$977.86	$977.80	$977.80