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	$36.41	5.741%	$38.5003	$38.50	$38.50	$38.50
Purchase #2	$196.78	4.831%	$206.2864	$206.29	$206.30	$206.30
Purchase #3	$42.87	5.174%	$45.0881	$45.09	$45.10	$45.10
Purchase #4	$197.53	4.748%	$206.9087	$206.91	$206.90	$206.90
Purchase #5	$153.78	11.611%	$171.6354	$171.64	$171.65	$171.60
Purchase #6	$17.57	7.377%	$18.8661	$18.87	$18.85	$18.90
Purchase #7	$31.87	4.766%	$33.3889	$33.39	$33.40	$33.40
7 purchase totals =	$676.81		$720.6739	$720.69	$720.70	$720.70