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	$38.56	10.755%	$42.7071	$42.71	$42.70	$42.70
Purchase #2	$234.81	6.408%	$249.8566	$249.86	$249.85	$249.90
Purchase #3	$89.36	12.385%	$100.4272	$100.43	$100.45	$100.40
Purchase #4	$94.75	13.365%	$107.4133	$107.41	$107.40	$107.40
Purchase #5	$180.54	9.360%	$197.4385	$197.44	$197.45	$197.40
Purchase #6	$203.54	13.287%	$230.5844	$230.58	$230.60	$230.60
Purchase #7	$163.86	6.687%	$174.8173	$174.82	$174.80	$174.80
7 purchase totals =	$1,005.42		$1,103.2444	$1,103.25	$1,103.25	$1,103.20