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	$50.62	9.434%	$55.3955	$55.40	$55.40	$55.40
Purchase #2	$249.34	13.309%	$282.5247	$282.52	$282.50	$282.50
Purchase #3	$181.83	8.204%	$196.7473	$196.75	$196.75	$196.70
Purchase #4	$223.65	3.557%	$231.6052	$231.61	$231.60	$231.60
Purchase #5	$191.25	13.349%	$216.78	$216.78	$216.80	$216.80
Purchase #6	$82.29	4.365%	$85.882	$85.88	$85.90	$85.90
Purchase #7	$194.92	13.395%	$221.0295	$221.03	$221.05	$221.00
7 purchase totals =	$1,173.90		$1,289.9642	$1,289.97	$1,290.00	$1,289.90