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	$84.58	5.690%	$89.3926	$89.39	$89.40	$89.40
Purchase #2	$196.65	9.704%	$215.7329	$215.73	$215.75	$215.70
Purchase #3	$240.72	5.795%	$254.6697	$254.67	$254.65	$254.70
Purchase #4	$59.29	12.302%	$66.5839	$66.58	$66.60	$66.60
Purchase #5	$121.70	8.642%	$132.2173	$132.22	$132.20	$132.20
Purchase #6	$41.98	3.131%	$43.2944	$43.29	$43.30	$43.30
Purchase #7	$43.74	3.307%	$45.1865	$45.19	$45.20	$45.20
7 purchase totals =	$788.66		$847.0773	$847.07	$847.10	$847.10