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	$192.29	3.207%	$198.4567	$198.46	$198.45	$198.50
Purchase #2	$40.75	8.742%	$44.3124	$44.31	$44.30	$44.30
Purchase #3	$36.79	8.772%	$40.0172	$40.02	$40.00	$40.00
Purchase #4	$81.43	11.597%	$90.8734	$90.87	$90.85	$90.90
Purchase #5	$190.30	13.667%	$216.3083	$216.31	$216.30	$216.30
Purchase #6	$36.69	8.603%	$39.8464	$39.85	$39.85	$39.80
Purchase #7	$178.25	6.611%	$190.0341	$190.03	$190.05	$190.00
7 purchase totals =	$756.50		$819.8485	$819.85	$819.80	$819.80