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	$248.42	4.135%	$258.6922	$258.69	$258.70	$258.70
Purchase #2	$147.83	12.128%	$165.7588	$165.76	$165.75	$165.80
Purchase #3	$147.38	5.250%	$155.1175	$155.12	$155.10	$155.10
Purchase #4	$11.84	10.306%	$13.0602	$13.06	$13.05	$13.10
Purchase #5	$123.43	3.569%	$127.8352	$127.84	$127.85	$127.80
Purchase #6	$79.71	3.833%	$82.7653	$82.77	$82.75	$82.80
Purchase #7	$34.96	3.703%	$36.2546	$36.25	$36.25	$36.30
7 purchase totals =	$793.57		$839.4838	$839.49	$839.45	$839.60