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	$172.90	4.706%	$181.0367	$181.04	$181.05	$181.00
Purchase #2	$141.90	12.765%	$160.0135	$160.01	$160.00	$160.00
Purchase #3	$59.59	9.249%	$65.1015	$65.10	$65.10	$65.10
Purchase #4	$138.50	5.177%	$145.6701	$145.67	$145.65	$145.70
Purchase #5	$39.46	3.534%	$40.8545	$40.85	$40.85	$40.90
Purchase #6	$67.62	4.477%	$70.6473	$70.65	$70.65	$70.60
Purchase #7	$19.43	7.588%	$20.9043	$20.90	$20.90	$20.90
7 purchase totals =	$639.40		$684.2279	$684.22	$684.20	$684.20