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	$142.64	4.464%	$149.0074	$149.01	$149.00	$149.00
Purchase #2	$79.29	12.460%	$89.1695	$89.17	$89.15	$89.20
Purchase #3	$73.52	9.555%	$80.5448	$80.54	$80.55	$80.50
Purchase #4	$50.90	10.122%	$56.0521	$56.05	$56.05	$56.10
Purchase #5	$196.65	12.840%	$221.8999	$221.90	$221.90	$221.90
Purchase #6	$137.60	4.395%	$143.6475	$143.65	$143.65	$143.60
Purchase #7	$35.98	3.284%	$37.1616	$37.16	$37.15	$37.20
7 purchase totals =	$716.58		$777.4828	$777.48	$777.45	$777.50