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	$108.83	13.841%	$123.8932	$123.89	$123.90	$123.90
Purchase #2	$73.67	12.508%	$82.8846	$82.88	$82.90	$82.90
Purchase #3	$49.40	12.493%	$55.5715	$55.57	$55.55	$55.60
Purchase #4	$192.47	4.597%	$201.3178	$201.32	$201.30	$201.30
Purchase #5	$78.73	8.564%	$85.4724	$85.47	$85.45	$85.50
Purchase #6	$117.96	11.524%	$131.5537	$131.55	$131.55	$131.60
Purchase #7	$107.96	13.547%	$122.5853	$122.59	$122.60	$122.60
7 purchase totals =	$729.02		$803.2785	$803.27	$803.25	$803.40