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	$239.33	12.716%	$269.7632	$269.76	$269.75	$269.80
Purchase #2	$246.76	9.641%	$270.5501	$270.55	$270.55	$270.60
Purchase #3	$140.51	12.290%	$157.7787	$157.78	$157.80	$157.80
Purchase #4	$226.30	13.522%	$256.9003	$256.90	$256.90	$256.90
Purchase #5	$131.40	4.156%	$136.861	$136.86	$136.85	$136.90
Purchase #6	$21.67	13.486%	$24.5924	$24.59	$24.60	$24.60
Purchase #7	$223.79	13.197%	$253.3236	$253.32	$253.30	$253.30
7 purchase totals =	$1,229.76		$1,369.7693	$1,369.76	$1,369.75	$1,369.90