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	$196.73	12.322%	$220.9711	$220.97	$220.95	$221.00
Purchase #2	$80.45	5.396%	$84.7911	$84.79	$84.80	$84.80
Purchase #3	$236.65	12.231%	$265.5947	$265.59	$265.60	$265.60
Purchase #4	$158.57	9.498%	$173.631	$173.63	$173.65	$173.60
Purchase #5	$65.77	10.802%	$72.8745	$72.87	$72.85	$72.90
Purchase #6	$119.54	10.799%	$132.4491	$132.45	$132.45	$132.40
Purchase #7	$101.54	13.768%	$115.52	$115.52	$115.50	$115.50
7 purchase totals =	$959.25		$1,065.8315	$1,065.82	$1,065.80	$1,065.80