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	$103.85	9.147%	$113.3492	$113.35	$113.35	$113.30
Purchase #2	$39.48	7.848%	$42.5784	$42.58	$42.60	$42.60
Purchase #3	$20.86	12.435%	$23.4539	$23.45	$23.45	$23.50
Purchase #4	$111.36	10.621%	$123.1875	$123.19	$123.20	$123.20
Purchase #5	$105.98	12.441%	$119.165	$119.17	$119.15	$119.20
Purchase #6	$176.68	13.699%	$200.8834	$200.88	$200.90	$200.90
Purchase #7	$36.90	12.326%	$41.4483	$41.45	$41.45	$41.40
7 purchase totals =	$595.11		$664.0657	$664.07	$664.10	$664.10