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	$171.69	4.654%	$179.6805	$179.68	$179.70	$179.70
Purchase #2	$194.87	5.339%	$205.2741	$205.27	$205.25	$205.30
Purchase #3	$87.83	13.846%	$99.9909	$99.99	$100.00	$100.00
Purchase #4	$101.46	12.399%	$114.04	$114.04	$114.05	$114.00
Purchase #5	$205.58	8.258%	$222.5568	$222.56	$222.55	$222.60
Purchase #6	$11.69	6.854%	$12.4912	$12.49	$12.50	$12.50
Purchase #7	$40.25	5.183%	$42.3362	$42.34	$42.35	$42.30
7 purchase totals =	$813.37		$876.3697	$876.37	$876.40	$876.40