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	$62.27	4.134%	$64.8442	$64.84	$64.85	$64.80
Purchase #2	$229.41	11.347%	$255.4412	$255.44	$255.45	$255.40
Purchase #3	$236.77	8.771%	$257.5371	$257.54	$257.55	$257.50
Purchase #4	$177.86	10.453%	$196.4517	$196.45	$196.45	$196.50
Purchase #5	$111.50	6.302%	$118.5267	$118.53	$118.55	$118.50
Purchase #6	$178.30	11.475%	$198.7599	$198.76	$198.75	$198.80
Purchase #7	$241.74	12.309%	$271.4958	$271.50	$271.50	$271.50
7 purchase totals =	$1,237.85		$1,363.0566	$1,363.06	$1,363.10	$1,363.00