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	$139.51	3.661%	$144.6175	$144.62	$144.60	$144.60
Purchase #2	$109.97	12.624%	$123.8526	$123.85	$123.85	$123.90
Purchase #3	$155.82	8.184%	$168.5723	$168.57	$168.55	$168.60
Purchase #4	$85.75	8.527%	$93.0619	$93.06	$93.05	$93.10
Purchase #5	$95.47	10.776%	$105.7578	$105.76	$105.75	$105.80
Purchase #6	$113.75	4.632%	$119.0189	$119.02	$119.00	$119.00
Purchase #7	$28.81	5.213%	$30.3119	$30.31	$30.30	$30.30
7 purchase totals =	$729.08		$785.1929	$785.19	$785.10	$785.30