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	$228.82	13.346%	$259.3583	$259.36	$259.35	$259.40
Purchase #2	$229.27	9.677%	$251.4565	$251.46	$251.45	$251.50
Purchase #3	$100.69	3.640%	$104.3551	$104.36	$104.35	$104.40
Purchase #4	$211.41	5.330%	$222.6782	$222.68	$222.70	$222.70
Purchase #5	$137.65	3.597%	$142.6013	$142.60	$142.60	$142.60
Purchase #6	$107.72	7.192%	$115.4672	$115.47	$115.45	$115.50
Purchase #7	$130.72	10.549%	$144.5097	$144.51	$144.50	$144.50
7 purchase totals =	$1,146.28		$1,240.4263	$1,240.44	$1,240.40	$1,240.60