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	$134.90	9.799%	$148.1189	$148.12	$148.10	$148.10
Purchase #2	$238.57	9.564%	$261.3868	$261.39	$261.40	$261.40
Purchase #3	$29.50	12.629%	$33.2256	$33.23	$33.25	$33.20
Purchase #4	$38.55	5.829%	$40.7971	$40.80	$40.80	$40.80
Purchase #5	$127.91	7.587%	$137.6145	$137.61	$137.60	$137.60
Purchase #6	$198.94	10.521%	$219.8705	$219.87	$219.85	$219.90
Purchase #7	$208.80	12.274%	$234.4281	$234.43	$234.45	$234.40
7 purchase totals =	$977.17		$1,075.4415	$1,075.45	$1,075.45	$1,075.40