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	$23.61	7.439%	$25.3663	$25.37	$25.35	$25.40
Purchase #2	$172.29	10.435%	$190.2685	$190.27	$190.25	$190.30
Purchase #3	$169.56	6.583%	$180.7221	$180.72	$180.70	$180.70
Purchase #4	$222.38	8.579%	$241.458	$241.46	$241.45	$241.50
Purchase #5	$180.43	13.360%	$204.5354	$204.54	$204.55	$204.50
Purchase #6	$48.28	13.460%	$54.7785	$54.78	$54.80	$54.80
Purchase #7	$91.54	12.125%	$102.6392	$102.64	$102.65	$102.60
7 purchase totals =	$908.09		$999.7680	$999.78	$999.75	$999.80