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	$36.56	13.267%	$41.4104	$41.41	$41.40	$41.40
Purchase #2	$112.55	5.787%	$119.0633	$119.06	$119.05	$119.10
Purchase #3	$99.50	4.380%	$103.8581	$103.86	$103.85	$103.90
Purchase #4	$249.65	11.146%	$277.476	$277.48	$277.50	$277.50
Purchase #5	$51.56	3.781%	$53.5095	$53.51	$53.50	$53.50
Purchase #6	$34.63	12.213%	$38.8594	$38.86	$38.85	$38.90
Purchase #7	$48.51	5.274%	$51.0684	$51.07	$51.05	$51.10
7 purchase totals =	$632.96		$685.2451	$685.25	$685.20	$685.40