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	$183.99	4.782%	$192.7884	$192.79	$192.80	$192.80
Purchase #2	$82.26	9.590%	$90.1487	$90.15	$90.15	$90.10
Purchase #3	$148.85	6.173%	$158.0385	$158.04	$158.05	$158.00
Purchase #4	$90.26	13.155%	$102.1337	$102.13	$102.15	$102.10
Purchase #5	$157.78	13.143%	$178.517	$178.52	$178.50	$178.50
Purchase #6	$71.48	12.661%	$80.5301	$80.53	$80.55	$80.50
Purchase #7	$41.27	4.703%	$43.2109	$43.21	$43.20	$43.20
7 purchase totals =	$775.89		$845.3673	$845.37	$845.40	$845.20