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	$144.28	8.452%	$156.4745	$156.47	$156.45	$156.50
Purchase #2	$151.92	12.786%	$171.3445	$171.34	$171.35	$171.30
Purchase #3	$176.28	7.861%	$190.1374	$190.14	$190.15	$190.10
Purchase #4	$92.32	8.777%	$100.4229	$100.42	$100.40	$100.40
Purchase #5	$22.52	13.351%	$25.5266	$25.53	$25.55	$25.50
Purchase #6	$237.46	4.347%	$247.7824	$247.78	$247.80	$247.80
Purchase #7	$222.35	12.286%	$249.6679	$249.67	$249.65	$249.70
7 purchase totals =	$1,047.13		$1,141.3562	$1,141.35	$1,141.35	$1,141.30