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	$184.95	9.642%	$202.7829	$202.78	$202.80	$202.80
Purchase #2	$108.83	13.590%	$123.62	$123.62	$123.60	$123.60
Purchase #3	$119.41	3.188%	$123.2168	$123.22	$123.20	$123.20
Purchase #4	$196.40	6.306%	$208.785	$208.79	$208.80	$208.80
Purchase #5	$103.94	5.284%	$109.4322	$109.43	$109.45	$109.40
Purchase #6	$129.54	7.710%	$139.5275	$139.53	$139.55	$139.50
Purchase #7	$22.50	9.202%	$24.5705	$24.57	$24.55	$24.60
7 purchase totals =	$865.57		$931.9349	$931.94	$931.95	$931.90