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	$38.51	8.696%	$41.8588	$41.86	$41.85	$41.90
Purchase #2	$161.67	11.271%	$179.8918	$179.89	$179.90	$179.90
Purchase #3	$69.46	12.523%	$78.1585	$78.16	$78.15	$78.20
Purchase #4	$99.27	12.798%	$111.9746	$111.97	$111.95	$112.00
Purchase #5	$79.69	13.646%	$90.5645	$90.56	$90.55	$90.60
Purchase #6	$223.30	6.239%	$237.2317	$237.23	$237.25	$237.20
Purchase #7	$163.43	8.334%	$177.0503	$177.05	$177.05	$177.10
7 purchase totals =	$835.33		$916.7302	$916.72	$916.70	$916.90