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	$185.32	12.772%	$208.9891	$208.99	$209.00	$209.00
Purchase #2	$77.61	7.778%	$83.6465	$83.65	$83.65	$83.60
Purchase #3	$94.85	7.481%	$101.9457	$101.95	$101.95	$101.90
Purchase #4	$131.88	3.538%	$136.5459	$136.55	$136.55	$136.50
Purchase #5	$199.34	9.747%	$218.7697	$218.77	$218.75	$218.80
Purchase #6	$118.89	7.219%	$127.4727	$127.47	$127.45	$127.50
Purchase #7	$38.81	10.664%	$42.9487	$42.95	$42.95	$42.90
7 purchase totals =	$846.70		$920.3183	$920.33	$920.30	$920.20