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	$28.65	10.199%	$31.572	$31.57	$31.55	$31.60
Purchase #2	$184.77	7.149%	$197.9792	$197.98	$198.00	$198.00
Purchase #3	$54.57	11.330%	$60.7528	$60.75	$60.75	$60.80
Purchase #4	$179.43	11.702%	$200.4269	$200.43	$200.45	$200.40
Purchase #5	$142.90	12.326%	$160.5139	$160.51	$160.50	$160.50
Purchase #6	$154.94	13.189%	$175.375	$175.38	$175.40	$175.40
Purchase #7	$40.76	3.365%	$42.1316	$42.13	$42.15	$42.10
7 purchase totals =	$786.02		$868.7514	$868.75	$868.80	$868.80